There was reluctance in his voice, compassion in his eyes. "Go on," I said harshly.
"There are two objections to your theory for which I can find no answer. One is that my own studies do not reveal any evidence of the kind of creature you have postulated. And I am led irrevocably to the conclusion that there would be tell-tale signs."
"And the other?" I whispered.
"The second objection is the manner in which this parasite actually came to earth—on a returning space ship. This we have from the aliens, themselves, according to what you overheard. This is the only way they could have got to earth. And yet that way is impossible."
I didn't want to ask why. The word was thick and hard and painful in my throat but I had to voice it. "Why? Why?"
"Your alien said something about transferring to another body—and you concluded that he meant this was necessary for the return trip through space to Mars. What is especially pertinent, he wanted to effect this transfer at the last possible moment when it would be too late for any close physical examination."
"Yes, one of them said something like that."
"And obviously, Mr. Cameron, we do not need the alien to give us the information that they would want to avoid close examination of the host. The presence of a powerful parasitical organism in man's body can quite readily be detected. We might not know what it was but we would know that it was there. We must assume that this would be particularly true in the case of a parasite so powerful that it was able to control directly the human body and mind. Any exhaustive examination would reveal the alien's existence in the body."
I felt the hope withering, turning brown and fragile.
"Mr. Cameron," Dr. Temple said quietly, "no parasite entered earth in the body of any of the men who came back. I need hardly tell you that each of those men was put through exhaustive, painstakingly complete physical and mental tests under rigidly controlled conditions, even before coming in contact with any humans back here on earth. You see, we had to be careful. There was the risk of bringing back deadly viruses that might not yet have visibly affected the men. There was the question of radiation, of contagious diseases, of any number of harmful effects. In addition, the very fact that these men had survived extensive space flight made them priceless subjects for study. Mr. Cameron, you needn't take my word for it, you can easily verify what I'm saying, but nothing unusual could have escaped the examination these men underwent." Dr. Temple swung toward the glass cases along the wall. "Why, even every bit of rock and bone and dead fungus you see in these cabinets was exhaustively examined and re-examined and tested with every means known to science before ever being touched by human hands!"