86 



Messrs. J. A. Gunn and R. St. A. Heathcote. 



among the most convenient to work with, for well-known reasons, are either 

 the snake venoms or one of the vegetable toxins, such as ricin. 



I have at various times begun such experiments with such samples of snake 

 venom as I could procure, but have been unable to complete them from want 

 of a suflBcient amount of a sufficiently active venom. All the experiments 

 have, of course, to be completed with the same sample of venom. I also tried 

 ricin, which was from one point of view more suitable, because in contra- 

 distinction to what is true of snake venoms it is extremely easy to immunise 

 rabbits to ricin. But unfortunately I found that ricin produced no effect on 

 the isolated heart or intestine of the rabbit, even in a concentration of 1 in 

 5000, although the minimum lethal dose of it for this animal was 0'05 mgrm. 

 per kilogramme. It was clearly unsuitable for this kind of investigation. 

 I found, however, that the red blood corpuscles of an animal immunised to 

 ricin are more easily agglutinated than are the red blood corpuscles of a 

 normal rabbit. 



Cushny, as has been pointed out, had found that the blood of a rabbit 

 immunised to 5000 times the minimum lethal dose of ricin still showed 

 agglutination like that of a normal rabbit, only it appeared even somewhat 

 more sensitive. As a matter of fact the increased sensitiveness is well 

 beyond experimental error. For example, I found by parallel experiments 

 that the washed corpuscles of a rabbit immunised to twenty minimum lethal 

 doses of ricin were agglutinated by 0*0005 per cent, of ricin as compared with 

 0'002 per cent, required to agglutinate washed corpusles of a normal rabbit. 

 Those observations suggested to me a doubt as to whether the red cells could 

 be a reliable index of acquired cellular immunity, presuming that such a 

 condition occurred. As has been pointed out above, they have certainly not 

 been found to be so in natural immunity, and a priori it is less likely that 

 they should be so in acquired immunity for these reasons. The mammalian 

 red cell is a cell that has lost its nucleus. It is probably not a living cell in 

 the ordinary sense at all but a mere box with a transitory existence. It is 

 difficult to imagine in what way \jh.e formed red cell could develop an increased 

 resistance in the process of immunisation. It is true that a more resistant 

 cell might be manufactured in the bone marrow and so be distributed into the 

 blood. But on the whole it seemed unwise to employ a cell that is, both 

 histologically and in regard to its passing existence, different from most 

 cells of the body as an index of what occurs, in the process of immunisation, 

 to the cells of the body generally. 



I am not suggesting — indeed the experiments of Camus and Gley and 

 Kossel point otherwise — that at no period in the course of immunisation will 

 an increased resistance be found in the red cells if the other cells of the body 



