NEUTRON EFFECTS ON ANIMALS 7 



marrow, the spleen, and lymphatic tissue. By giving a sufficient dose of 

 neutrons it is possible to abolish all white blood corpuscles from the blood, 

 and it may even be possible after a large dose of neutrons to find bone mar- 

 row without a single leukocyte. Use is made of this extraordinary fact 

 by taking the level of the white blood cell count as a measure of the amount 

 of injury produced by the neutrons. It is a test easy to do and familiar to 

 laboratory technicians. It is by no means exact because it is influenced 

 by other factors: resistance, age, etc. 



The reduction and even disappearance of the white blood cells does not 

 seem to be dependent upon direct killing of these cells, for untreated white 

 blood cells, introduced after exposure to neutrons, live for some time and 

 are not directly killed by repeated radiation. Something happens which 

 prevents the continued production of these short-lived, easily reconstructed cells. 

 It is as if a population ceased to be fertile and produced no offspring: they 

 live their life and at the end are not any more. 



Such a result in such short-lived cells is significant of the disruption 

 of the processes of their reproduction. If the dose of neutrons is not so 

 great, recovery may take place in time. There is a possibility of the re- 

 crudescence of the specific vital factor which is necessary to their con- 

 tinuance. 



In consideration of the mechanism of neutron action, it is futile to speak 

 in terms of ionization when there is no idea of where in the vital system that 

 ionization exists. Is it in the nucleus, the cell, the cell boundary, or the 

 membrane? It is true that the greater the amount of neutrons applied 

 the greater the results, but such an amount of energy, hundreds of times 

 that of the short utraviolet line 2536 A, has comparatively less efficiency 

 as a lethal instrument. 



A word should be said about the variability of experimental animals. 

 Chemists and physicists without much experience in animal experimenta- 

 tion are apt to think of them as exact systems, similar to those of the sci- 

 ences in which they work and in which there are definite quantitative 

 measurements. Not only are different species of animals different in their 

 reactions, but different strains of the same species vary in their reactions. 

 There are strains of mice which have naturally occurring cancer and strains 

 that are cancer-resistant. There are strains of rats that are resistant to 

 transplanted cancer and those that are not. The same is true of many 

 other qualities: age, diet, and even environment may alter their reactions. 



Then too, the vital system is a dynamic system: Its chief purpose is life 

 and it goes on living. Alterations in one or other phase will upset the 

 system, but this cannot be explained in terms of such exactitude as exists 

 in chemical and ph^'sical experiments. The distinguishing phases of vital 

 systems are that they are provided with the means for the rapid attainment 



