"How about you two?", snapped Mr. Sharpe. He pointed to the back, where Mary and Davy Lockett were sitting. Davy, the younger of the two, was busy trying to bury his face in his textbook and not get noticed by anyone, but his sister grabbed his hand and pulled him to the front.
"Okay, which of you wants to hold Chad down while I give the shots?"
Mary eagerly came forward and put her soft hands on Chad's muzzle, one under his snout and the other behind one of his floppy ears. He seemed to like it, as his leg briefly slapped against the table in pleasure. Taking the opportunity, Rick quickly administered all three shots.
"There. Now he's relaxed, his erection will last as long as it we need it to, and he won't feel a thing when we clip his balls off. Now, we need to get to work, and fast. Mary, he seems to like you. I don't suppose you know how to jerk a dog off?"
Mary shook her head. "Well, the good news is it isn't that much different from jerking off your boyfriend. First, you need to peel away his foreskin, then grab his shaft. It'll feel a little like touching raw meat, but trust me, you'll get used to it. Davy, since you're not being very useful, grab this beaker and cover his tip. We can't afford to lose a single drop."
Mary carefully pulled back Chad's foreskin, and started tugging on his cock. By now, Chad was pretty much just a large, semi-human dog, and could only make pitiful noises as he felt Mary milk him. After a few minutes, he shot his load into the beaker, all thick and white and creamy. Mary started again, and he came a second time. She continued until Chad started pawing at her hand and letting out a few whimpers and growls, as if to say that he was done. By then, the beaker was nearly two-thirds full with his semen.
Rick took the beaker, covered it, and stashed it in the lab's special deep cooling fridge. "We'll save that for later. Right now, we need to neuter him before his testes make more sperm. Davy, help me with this. Mary, lay him down and keep his occupied."
Mary motioned for Chad to lay on his stomach, and he complied, fully trusting her. As she stroked his head and whispered what a good brave boy he was being, Rick and Davy slipped behind and motioned the class to be completely silent. Rick then retrieved his cutting tools from a sterile pouch. He lowered himself under Chad's rear end, where his balls were dangling in a droopy sack of skin that hung freely near his tail.
With great skill, Rick, with a square of fabric at his feet as a towel, made an opening in the sack, cut and extracted Chad's two large testicles, and placed them into a secure box held by Davy, who managed not to faint. He then sewed up the skin, before cleaning up and placing the tools back in their pouch and the box in the fridge. The whole affair had lasted less than an hour.
Chad was so comfortable, and numb from the shot, that he didn't even notice his balls were gone until he suddenly stood up on all fours and looked between his legs at the empty flap of skin. Rick happily slapped his rear. "Congratulations, Chad. No infections or complications, and you won't father a single mongrel or mutt. Mary, give him a treat for being such a good patient."
Chad ate the treat she gave him, but sorrow filled his heart. He was now, and forever, a dog.