258 PRINCIPLES OF GENERAL PHYSIOLOGY 



not u lecithin like substance, nor like Funk's " vitauiines," to be mentioned 

 presently. The fact that it is soluble in fat does not, of course, necessitate 

 the conclusion that it is of fatty nature. Funk's vitamine must belong to another 

 class of substances, or, more probably, the nitrogenous substance which lie 

 has analysed is not the really active one. 



The experiments of Osborne, Mendel, and Ferry (1912, 1) prove undoubtedly 

 that a protein as unlike the tissue proteins as gliadin is, can .serve for the purpose 

 of forming new tissues, through the intervention qf the adult animal. The 

 experiments given on pp. 485 and 486 of their paper are instructive. A rat 

 was fed for 178 days on a diet consisting of gliadin only as protein, along with 

 protein-free milk, carbohydrate, and fat ; at the end of this time, four young 

 rats were born. Of these, after thirty days' feeding by the mother's milk, 

 three were put on a normal diet while the fourth received gliadin food similar 

 to that which the mother had been receiving all the time. The three former 

 grew well, but the latter quickly began to fail. The diet which sufficed for the 

 adult, not only for its own maintenance, but also for production of young 

 and secretion of normal milk, was insufficient for the growth of the young 

 animal. It will be noticed that the requisite substances were present in 

 the milk secreted by the mother, since, while fed on this, the young rats 

 showed normal growth. The adult, therefore, has the power of forming some 

 substances out of others in the diet, which power is not possessed by the young 

 animal, so that they must be supplied to it from without. It will be seen 

 that these experiments do not altogether decide the question as to whether the 

 failure to grow was due to want of lysine in the diet or to want of some 

 " accessory factor." The fact that when casein was substituted for gliadin, the 

 diet was adequate, indicates that the former was the case. 



In a later paper, Osborne, Mendel, and Ferry (1912, p. 242) come to the conclusion that 

 maintenance is possible in the absence of any " hormone " element, since the diet was 

 extracted to remove such substances. Whether this conclusion is justified seems doubtful 

 from the experiments of Hopkins and Neville (1913), who repeated the experiments in 

 question. The rats fed in this way ceased to grow almost at once and, after a brief period in 

 which no loss of weight occurred, steadily declined and, with the exception of four out of 

 twenty-four animals, died before the fortieth day. These observers are inclined to think that 

 a trace of the active substance may have remained in Osborne and Mendel's diet. It is clear 

 ttiat conclusions must be drawn very cautiously from results which might be due to such 

 extraordinarily minute quantities of unextracted matter. 



We must not forget that there is no reason to suppose that the diet, containing 

 amino-acids as sole source of nitrogen, which was found by Loewi and others to be 

 capable of maintenance, or even a certain degree of laying on of protein, was free 

 from the " accessory factors " in question, since uuextracted carbohydrate was added 

 to the food. 



There is, on the whole, considerable evidence that a diet, wanting in something 

 necessary for yrwvlh, may nevertheless be capable of keeping up the general 

 condition in a normal manner. An interesting and, if confirmed, pract it-ally 

 important application of this fact is reported by Sweet, Ooraon- White, and Saxon 

 (1913). Since tumours, such as cancer, are growths, it seemed that it should be 

 possible to retard their increase by a diet insufficient for growth, while adequate 

 for maintenance. The experiments showed that mice, fed on well-washed gluten 

 from wheat, together with starch, lard, lactose, and salts, could be kept at a 

 constant weight, that is, without growth, for thirty days or more. Comparing 

 animals on this diet, inoculated with a rapidly growing tumour at the same time 

 as those on normal diet, a considerable dift'ereiu -e \\as found in the rate of growth 

 of the tumour, which was much slower in those on the restricted diet. One 

 mouse, for example, on restricted diet, at fifty-two days after inoculation, had 

 at this time a scarcely visible tumour of 4 mm. in diameter. The mouse was then 

 put on normal diet of bread, corn, etc., and, thirty days later, the tumour was 

 nearly as big as the mouse itself. Prof. Hopkins informs me that he had already, 

 before 1913, obtained similar results. 



We may next consider shortly the results obtained by various observers, with 

 respect to certain diseases produced by the absence of some substances of a similai 



