I leaned into the car, tucked some papers under the dog's head, injected the apomorphine and waited.

The man looked at me with anxious eyes. "What is it?"

"Strychnine poisoning, Mr. Bartle. I've just given an emetic to make him vomit." As I spoke the animal brought up the contents of his stomach on to the paper.

"Will that put him right?"

"It depends on how much of the poison has been absorbed." I didn't feel like telling him that it was almost invariably fatal, that in fact I had treated six dogs in the last week with the same condition and they had all died. "We'll just have to hope."

He watched me as I filled another syringe with barbiturate. "What are you doing now?"

"Anaesthetising him." I slipped the needle into the radial vein and as I slowly trickled the fluid into the dog's bloodstream the taut muscles relaxed and he sank into a deep slumber.

"He looks better already," Mr. Bartle said.

"Yes, but the trouble is when the injection wears off he may go back into a spasm. As I say, it all depends on how much of the strychnine has got into his system. Keep him in a quiet place with as little noise as possible. Any sound can bring on a spasm. When he shows signs of coming out of it give me a ring."

I went back into the house. Seven cases in a week! It was tragic and scarcely believable, but there was no doubt left in my mind now. This was malicious. Some psychopath in our little town was deliberately putting down poison to kill dogs. Strychnine poisoning was something that cropped up occasionally. Gamekeepers and other people used the deadly drug to kill vermin, but usually it was handled with great care and placed out of reach of domestic pets. Trouble started when a burrowing dog came across the poison by accident. But this was different.

I had to warn pet owners somehow. I lifted the 'phone and spoke to one of the reporters on the Darrowby and Houlton Times. He promised to put the story in the next edition, along with advice to keep dogs on their leads and otherwise supervise pets more carefully.

Then I rang the police. The sergeant listened to my account. "Right Mr. Herriot, I agree with you that there's some crackpot going around and we'll certainly investigate this matter. If you'll just give me the names of the dog owners involved ... thank you ... thank you. We'll see these people and check round the local chemists to see if anybody has been buying strychnine lately. And of course we'll keep our eyes open for anybody acting suspiciously."

I came away from the 'phone feeling that I might have done something to halt the depressing series of events, but I couldn't rid myself of a gloomy apprehension that more trouble was round the corner. But my mood lightened when I saw Johnny Clifford in the waiting room.

Johnny always made me feel better because he was invariably optimistic and wore a cheerful grin which never altered, even though he was blind. He was about my own age and he sat mere in his habitual pose, one hand on the head of his guide dog, Fergus.

"Is it inspection time again already, Johnny?" I asked.

"Aye, it is that Mr. Herriot it's come round again. It's been a quick six months." He laughed and held out his card.

I squatted and looked into the face of the big Alsatian sitting motionless and dignified by his master's side. "Well, and how's Fergus these days?"

"Oh he's in grand fettle. Eatin' well and full of life." The hand on the head moved round to the ears and at the other end the tail did a bit of sweeping along the waiting-room floor.

As I looked at the young man, his face alight with pride and affection, I realised afresh what this dog meant to him. He had told me that when his failing sight progressed to total blindness in his early twenties he was filled with a despair which did not lessen until he was sent to train with a guide dog and met Fergus; because he found something more than another living creature to act as his eyes, he found a friend and companion to share every moment of his days.

"Well, we'd better get started," I said. "Stand up a minute, old lad, while I take your temperature." That was normal and I went over the big animal's chest with a stethoscope, listening to the reassuringly steady thud of the heart As I parted the hair along the neck and back to examine the skin I laughed.

"I'm wasting my time here, Johnny. You've got his coat in perfect condition."

"Aye, never a day goes by but he gets a good groomin'."

I had seen him at it, brushing and combing tirelessly to bring extra lustre to the sleek swathes of hair. The nicest thing anybody could say to Johnny was, "That's a beautiful dog you've got." His pride in that beauty was boundless even though he had never seen it himself.

Treating guide dogs for the blind has always seemed to me to be one of a veterinary surgeon's most rewarding tasks. To be in a position to help and care for these magnificent animals is a privilege, not just because they are highly trained and valuable but because they represent in the ultimate way something which has always lain near the core and centre of my life: the mutually depending, trusting and loving association between man and animal.

Meeting these blind people was a humbling experience which sent me about my work with a new appreciation of my blessings.

I opened the dog's mouth and peered at the huge gleaming teeth. It was dicing with danger to do this with some Alsatians, but with Fergus you could haul the great jaws apart and nearly put your head in and he would only lick your ear. In fact he was at it now. My cheek was nicely within range and he gave it a quick wipe with his large wet tongue.

"Hey, just a minute, Fergus!" I withdrew and plied my handkerchief. "I've had a wash this morning. And anyway, only little dogs lick-not big tough Alsatians."

Johnny threw back his head and gave a great peal of laughter. "There's nowt tough about him, he's the softest dog you could ever meet."

"Well, that's the way I like them," I said. I reached for a tooth scaler. "There's just a bit of tartar on one of his back teeth. I'll scrape it off right now."

When I had finished I looked in the ears with an auroscope. There was no canker but I cleaned out a little wax.

Then I went round the feet, examining paws and claws. They always fascinated me, these feet; wide, enormous, with great spreading toes. They had to be that size to support the big body and the massive bones of the limbs.

"All correct except that one funny claw, Johnny."

"Aye, you allus have to trim that 'un, don't you? I could feel it was growin' long again."

"Yes, that toe seems to be slightly crooked or it would wear down like the others with all the walking he does. You have a great time going on walks all day, don't you, Fergus?"

I dodged another attempted lick and closed my clippers around the claw. I had to squeeze till my eyes popped before the overgrown piece shot away with a loud crack.

"By gosh, we'd go through some clippers if all dogs had claws like that," I gasped. "It just about does them in every time he calls."

Johnny laughed again and dropped his hand on the great head with that gesture which said so much.

I took the card and entered my report on the dog's health along with the things I had done. Then I dated it and handed it back. "That's it for this time, Johnny. He's in excellent order and there's nothing more I need do to him."

"Thank you, Mr. Herriot. See you next time round, then." The young man took hold of the harness and I followed the two of them along the passage and out of the front door. I watched as Fergus halted by the kerb and waited till a car had passed before crossing the road. They hadn't gone very far along the road when a woman with a shopping bag stopped them. She began to chatter animatedly, looking down repeatedly at the big dog. She was talking about Fergus and Johnny rested his hand on the noble head and nodded and smiled. Fergus was his favourite topic.

Shortly after midday Mr. Bartle rang to say Jasper showed signs of returning spasms and before sitting down to lunch I rushed round to his house and repeated the barbiturate injection. Mr. Bartle owned one of the local mills, producing cattle food for the district. He was a very bright man indeed.

"Mr. Herriot," he said. "Please don't misunderstand me. I have every faith in you, but isn't there anything else you can do? I am so very fond of this dog."

I shrugged helplessly. "I'm sorry, but I can't do any more."

"But is there no antidote to this poison?"

"No, I'm afraid there isn't."

"Well ..." He looked down with drawn face at the unconscious animal. "What's going on? What's happening to Jasper when he goes stiff like he did? I'm only a layman but I like to understand things."

"I'll try to explain it," I said. "Strychnine is absorbed into the nervous system and it increases the conductivity of the spinal cord."

"What does that mean?"

"It means that the muscles become more sensitive to outside stimuli so that the slightest touch or sound throws them into violent contractions."

"But why does a dog stretch out like that?"

"Because the extensor muscles are stronger than the flexors, causing the back to be arched and the legs extended."

He nodded. "I see, but ... I believe it is usually fatal. What is it that ... kills them?"

"They die of asphyxia due to paralysis of the respiratory centre or contraction of the diaphragm."

Maybe he wanted to ask more, but it was painful for him and he stayed silent.

"There's one thing I'd like you to know, Mr. Bartle," I said. "It is almost certainly not a painful condition."

"Thank you." He bent and briefly stroked the sleeping dog. "So nothing more can be done?"

I shook my head. "The barbiturate keeps the spasms in abeyance and we'll go on hoping he hasn't absorbed too much strychnine. I'll call back later, or you can ring me if he gets worse. I can be here in a few minutes."

Driving away, I pondered on the irony that made Darrowby a paradise for dog killers as well as dog lovers. There were grassy tracks everywhere; wandering by the river's edge, climbing the fell-sides and coiling green and tempting among the heather on the high tops. I often felt sympathy for pet owners in the big cities, trying to find places to walk their dogs. Here in Darrowby we could take our pick. But so could the poisoner. He could drop his deadly bait unobserved in a hundred different places.

I was finishing the afternoon surgery when the 'phone rang. It was Mr. Bartle.

"Has he started the spasms again?" I asked.

There was a pause. "No, I'm afraid Jasper is dead. He never regained consciousness."

"Oh ... I'm very sorry." I felt a dull despair. That was the seventh death in a week.

"Well, thank you for your treatment, Mr. Herriot. I'm sure nothing could have saved him."

I hung up the 'phone wearily. He was right. Nothing or nobody could have done any good in this case, but it didn't help. If you finish up with a dead animal there is always the feeling of defeat.

Next day I was walking on to a farm when the farmer's wife called to me. "I have a message for you to ring back to the surgery."

I heard Helen's voice at the other end. "Jack Brimham has just come in with his dog. I think it's another strychnine case."

I excused myself and drove back to Darrowby at top speed. Jack Brimham was a builder. He ran a one-man business and whatever job he was on-repairing roofs or walls or chimneys-his little white rough-haired terrier went with him, and you could usually see the little animal nosing among the piles of bricks, exploring in the surrounding fields.

Jack was a friend, too. I often had a beer with him at the Drovers' Arms and I recognised his van outside the surgery. I trotted along the passage and found him leaning over the table in the consulting room. His dog was stretched there in that attitude which I dreaded.

"He's gone, Jim," he muttered.

I looked at the shaggy little body. There was no movement, the eyes stared silently. The legs, even in death, strained across the smooth surface of the table. It was pointless, but I slipped my hand inside the thigh and felt for the femoral artery. There was no pulse.

"I'm sorry, Jack," I said.

He didn't answer for a moment. "I've been readin' about this in the paper, Jim, but I never thought it would happen to me. It's a bugger, isn't it?"

I nodded. He was a craggy-faced man, a tough Yorkshireman with a humour and integrity which I liked and a soft place inside which his dog had occupied. I did not know what to say to him.

"Who's doin' this?" he said, half to himself.

"I don't know, Jack. Nobody knows."

"Well I wish I could have five minutes with him, that's all." He gathered the rigid little form into his arms and went out.

My troubles were not over for that day. It was about 11 p.m. and I had just got into bed when Helen nudged me.

"I think there's somebody knocking at the front door, Jim."

I opened the window and looked out. Old Boardman, the lame veteran of the first war who did odd jobs for us, was standing on the steps.

"Mr. Herriot," he called up to me. "I'm sorry to bother you at this hour, but Patch is ill."

I leaned further out. "What's he doing?"

"He's like a bit o' wood-stiff like, and laid on 'is side."

I didn't bother to dress, just pulled my working corduroys over my pyjamas and went down the stairs two at a time. I grabbed what I needed from the dispensary and opened the front door. The old man, in shirt sleeves, caught at my arm.

"Come quickly, Mr. Herriot!" He limped ahead of me to his little house about twenty yards away in the lane round the corner.

Patch was like all the others. The fat spaniel I had seen so often waddling round the top yard with his master was in that nightmare position on the kitchen floor, but he had vomited, which gave me hope. I administered the intravenous injection but as I withdrew the needle the breathing stopped.

Mrs. Boardman, in nightgown and slippers, dropped on her knees and stretched a trembling hand towards the motionless animal.

"Patch ..." She turned and stared at me, wide-eyed. "He's dead!"

I put my hand on the old woman's shoulder and said some sympathetic words. I thought grimly that I was getting good at it. As I left I looked back at the two old people. Boardman was kneeling now by his wife and even after I had closed the door I could hear their voices: "Patch ... oh Patch."

I almost reeled over the few steps to Skeldale House and before going in I stood in the empty street breathing the cool air and trying to calm my racing thoughts. With Patch gone, this thing was getting very near home. I saw that dog every day. In fact all the dogs that had died were old friends-in a little town like Darrowby you came to know your patients personally. Where was it going to end?

I didn't sleep much that night and over the next few days I was obsessed with apprehension. I expected another poisoning with every 'phone call and took care never to let my own dog, Sam, out of the car in the region of the town. Thanks to my job I was able to exercise him miles away on the summits of the fells, but even there I kept him close to me.

By the fourth day I was beginning to feel more relaxed. Maybe the nightmare was over. I was driving home in the late afternoon past the row of grey cottages at the end of the Houlton Road when a woman ran waving into the road.

"Oh, Mr. Herriot," she cried when I stopped. "I was just goin' to t'phone box when I saw you."

I pulled up by the kerb. "It's Mrs. Clifford, isn't it?"

"Yes, Johnny's just come in and Fergus 'as gone queer. Collapsed and laid on t'floor."

"Oh no!" An icy chill drove through me and for a moment I stared at her, unable to move. Then I threw open the car door and hurried after Johnny's mother into the end cottage. I halted abruptly in the little room and stared down in horror. The very sight of the splendid dignified animal scrabbling helplessly on the linoleum was a desecration, but strychnine is no respecter of such things.

"Oh God!" I breathed. "Has he vomited, Johnny?"

"Aye, me mum said he was sick in t'back garden when we came in." The young man was sitting very upright in a chair by the side of his dog. Even now there was a half smile on his face, but he looked strained as he put out his hand in the old gesture and failed to find the head that should have been there.

The bottle of barbiturate wobbled in my shaking hand as I filled the syringe. I tried to put away the thought that I was doing what I had done to all the others-all the dead ones. At my feet Fergus panted desperately, then as I bent over him he suddenly became still and went into the horrible distinctive spasm, the great limbs I knew so well straining frantically into space, the head pulled back grotesquely over the spine.

This was when they died, when the muscles were at full contraction. As the barbiturate flowed into the vein I waited for signs of relaxation but saw none. Fergus was about twice as heavy as any of the other victims I had treated and the plunger went to the end of the syringe without result.

Quickly I drew in another dose and began to inject it, my tension building as I saw how much I was administering. The recommended dose was 1 cc per 5 lb. body weight and beyond that you could kill the animal. I watched the gradations on the glass barrel of the syringe and my mouth went dry when the dose crept far beyond the safety limit. But I knew I had to relieve this spasm and continued to depress the plunger relentlessly.

I did it in the grim knowledge that if he died now I would never know whether to blame the strychnine or myself for his death.