Growth-Determining Substances. 227 



contains the "Y" factor. This can be concentrated on the water 

 bath to a small bulk, filtered from tyrosine after standing over- 

 night on ice, and concentrated further with the addition of al- 

 cohol, to beginning crystallization. On standing, crystals separate 

 consisting of microscopic spheres apparently made up of finely 

 interwoven needles. These crystals are exceedingly soluble in 

 water, and quite soluble even in 70 to 80 per cent, alcohol, and 

 there is considerable loss on recrystallization. In one prepara- 

 tion the yield after one recrystallization from strong alcohol was 

 0.012 g. from 200 g. aminoids. Growth was given with 0.000,01 g. 

 of these crystals in 25 c.c. of media. Further recrystallization 

 apparently either eliminates the active factor from the main 

 bulk of crystals, or else alters the chemical nature of the substance, 

 since growth becomes very slow and scanty. The mother liquors, 

 still containing considerable quantities of crystalline material, 

 together with some amorphous brown substance, likewise show 

 diminished activity, so that there is probably in the case of the 

 "Y" factor, as with the "X," a certain amount of lability as the 

 preparations become purer. I do not wish to state definitely at 

 this time the belief that the crystals just described are in fact the 

 active "Y" material, and further work with larger quantities 

 must be done. There is, indeed, no assurance that the crystals 

 are pure because of the difficulty in recrystallizing caused by the 

 high solubility. 



After two recrystallizations, the crystals when dried at ioo° 

 are light and powdery. They give a moderately strong reaction 

 with Folin's phenol reagent, but no color with the nitro-prusside 

 test. Nitrogen is present to the amount of 10.6 per cent, by the 

 micro-kjeldahl method, and qualitative tests for sulphur are 

 positive after fusion with sodium, but the lead-acetate test on 

 boiling with NaOH is negative. Phosphorus and halogens are 

 not found. Sufficient material for complete quantitative analysis 

 has not yet been prepared. 



In the first report on this work, it was stated that the hydro- 

 lysates of certain proteins, such as gelatine, were not capable of 

 reactivating the infusion. At that time, it was not recognized 

 that two substances were involved, and in the light of that fact, 

 a further investigation should be made as to whether those pro- 



