TRANSMISSION OF TROPICAL DISEASES. 19 



it has thrown light on two other diseases not exactly tropical. 

 The first of these is Scurvy, which we are wont to associate 

 with Arctic expeditions. This disease also is a deficiency 

 disease, for scurvy can readily be produced in guinea-pigs 

 by feeding them exclusively on bread. It is not simply a 

 case of starvation, for guinea-pigs may be starved by feeding 

 on cabbage alone, but they show no signs of scuivy. There 

 is an absence of something in the bread diet which they require. 

 What it is, we do not know. This hypothetical body we call a 

 vitamine. In all probability another deficiency disease is 

 Rickets, a disease characterised by a failure of ossification 

 in the bones. The disease is cured by change of diet. The 

 ordinary process of growth is also dependent on the presence 

 of these, at present mysterious, bodies, "growth vitamines " 

 as we may call them. Rats, e.g., will not thrive on an artificially 

 purified diet, but if a quantity of milk equal to only 1 per cent, 

 of the artificial food be added, growth proceeds normally. 

 This last fact raises a very important question. Growth 

 we have seen is dependent on a vitamine. Now cancer is a 

 pathological growth, and in all probability this growth is 

 also a dependent on a vitamine. Now if the vitamines for 

 ordinary and cancerous growths were different, it might be 

 possible to construct a diet which would exclude the cancer 

 vitamine, but this is visionary, for we are at present only at 

 the beginning of our knowledge of vitamines. I would claim, 

 then, that tropical medicine in this matter has not only extended 

 its own sphere of knowledge, but has been of distinct service 

 to medicine of temperate climes. 



