446 Dr. W. Marcet on the Nutrition of 



subsequently by Bert {Leqons sur la Physiologie comparee de la 

 Respiration, ])ar Paul Bert, 1870). By passing through the sub- 

 stance of the lung-tissue, carbonic acid must combine with what- 

 ever free potash and soda it may contain, and consequently 

 transform most of the potash into crystalloid carbonate of potash • 

 the potash is therefore removed as phosphate and carbonate, but 

 mostly as carbonate ; while in the case of muscular tissue, the 

 potash is entirely eliminated as phosphate. 



Now, does the colloid condition of phosphoric acid and potash 

 found in animal tissues exist in soil, or only in plants ? This 

 is a very interesting question, open to investigation. One thing 

 is certain — that the liquid excreta of animals and other liquid 

 manures are, as a rule, crystalloids. Plants take up the material 

 they require in quantities which have no relation with equivalent 

 proportions, thereby forming colloids; thus, if soil should con- 

 tain phosphate of soda and soluble potash salts, plants will take 

 up phosphoric acid and potash in quantities utterly at variance 

 with their equivalent weights, leaving behind nearly the whole of 

 the soda as carbonate and chloride. But I have also reason to 

 believe that crystalloid mixtures are transformed, to some extent, 

 into colloids in the earth. 



On the Colloid Condition of Plants. 



As a rule, the mineral constituents of plants are very much 

 the same as those of animal tissues ; they mostly consist of 

 phosphoric acid, potash, and magnesia, and are very poor in 

 chloride of sodium. Now phosphoric acid and potash are 

 found in a great measure in the colloid state in vegetable as w'ell as 

 in animal tissues. The vegetables 1 have examined are wheat 

 or w^heaten flour, potato, and rice, selecting those mostly used 

 as food for man. It is remarkable that, although the total 

 amount of phosphoric acid and potash they contain varies, 

 still vve find, after dialyzing for twenty-four hours a mixture 

 of these materials with water, the same or nearly the same 

 relation to exist between the colloid and total phosphoric acid 

 and the colloid and total potash respectively m each of them. 

 The analysis was conducted in the following way. 100 

 grammes, say, of wheateu flour, were mixed with enough dis- 

 tilled water for the whole to be nearly liquid ; and this was 

 placed in a dialyzer which was floated for twenty-four hours over 

 a bulk of water equal to eight or ten times that of the contents 

 of the dialyzer. After that lapse of time the volumes of the con- 

 tents of the dialyzer and of the solution outside were determined. 

 The material in the dialyzer was then dried and incinerated, and 

 the ash was analyzed for the determination of the phosphoric 

 acid and potash. On the other hand, a certain quantity of the 



