158 MacDOUGAL and SPOEHR— COMPONENTS AND 



The effect of the hydrogen ions which are present in a concen- 

 tration of pH^3 in the acid solution is to induce a high swelhng 

 in gelatine and to produce a lessened swelling as this component is 

 lessened and as the carbohydrate is increased. A finely parallel 

 series was obtained in tests of living sections of Opuntia from last 

 December to March in which the proportionate swelling in acid 

 varied from 80 per cent, in December to 'j'j in January, 7 in Febru- 

 ary, rising to 78 in March and falling to 64 in April, as compared 

 with water at 100. The course of the pentosans was not followed 

 at the same time, but in a previous year the variation in the pentosan 

 content of similar material was from 10 in late December to 4.7 in 

 mid- January, 6 in mid-February, and to 5.5 late in March, which 

 allowing for seasonal differences, gives a fair parallel. 



The hydroxide is seen to cause a swelling of both agar and of 

 gelatine less than in water, and to cause a swelling of gelatine some- 

 thing less than in acid. Its general effect is to lessen hydration as 

 the carbohydrate component of the biocolloid becomes greater, al- 

 though an aberrant high swelling is shown by mixtures of equal 

 parts of gelatine and agar. 



Turning now to the plant material which shows the seasonal 

 variation of pentosans noted above the swelling of living material 

 varies from comparative values of 100 in December, 103 in January, 

 100 in February, and no in March, facts in no wise discordant with 

 the seasonal changes and probable accumulation of metallic salts in 

 the cells. 



Glycocoll produces a maximum effect on agar and a minimum 

 on gelatine or the albuminous component of biocolloids. Its maxi- 

 mum accelerating effect seems to be upon mixtures containing 25 to 

 40 per cent, of the carbohydrate, although in all cases it causes agar 

 mixtures to hydrate to a point beyond that which might be reached 

 in water. 



If we now seek to ascertain what type of biocolloid is capable of 

 the greatest average hydration or growth under the influence of 

 these substances and of the basic histidine, it will be found in a 

 mixture which is composed of i part carbohydrate and 3 parts al- 

 buminous material. Biocolloids containing more carbohydrate than 

 albuminous matter would be most sensitive to the presence of hy- 



