492 APPENDIX. 



from the separated crystals which, when the stream of carbonic acid 

 is interrupted, gradually sink to the bottom, and form a consi- 

 derable bright vermilion-coloured sediment. Much the same method 

 must be employed to obtain the prismatic crystals from human 

 blood or the blood of cats and dogs ; but in this case it is neces- 

 sary to have recourse to several other conditions, which will sub- 

 sequently be noticed. These crystals may indeed be separated 

 by rinsing from all the constituents of the serum and from the 

 greater part of the colourless blood-corpuscles, as well as from 

 the cell-membranes of the coloured corpuscles, but still, notwith- 

 standing repeated rinsings, many of the latter frequently remain, 

 in consequence of having served, to a certain extent, as points of 

 deposite for the crystals which thus enclose them ; and hence they 

 are not adapted, when in this condition, for elementary analysis. 

 They must therefore be dissolved in water, and carefully filtered, 

 in order perfectly to free them from all morphological particles. 

 The re-crystallisation, however, presents great difficulties. We 

 will here merely observe, that we cannot employ a high degree 

 of heat on account of the coagulability of the substance, or the 

 air-pump on account of the amount of gas necessary for crystal- 

 lisation. We may, moreover, recognise that the solution before us 

 is that of a pure crystalline substance, from the fact that it cannot 

 be precipitated by bichloride of mercury, nitrate of silver, or 

 basic acetate of lead. The coagulum, which is obtained by heat 

 from the crystalline solution, is at all events so far unsuited to 

 elementary analysis, that it does not represent the pure crystalline 

 substance ; for during coagulation the crystalline substance loses 

 not only carbonic acid and phosphates, but also about l'2{j- of 

 organic matter, which consists of a strongly re-acting acid and of 

 a nitrogenous body, bearing some remote resemblance to glutin. 



The numerous and variously modified experiments which I 

 have instituted on this subject, lead me to regard light merely as 

 an auxiliary in the crystallisation ; for although crystals are 

 certainly also formed in the dark, or even in the night under 

 otherwise similar conditions, they are only gradually deposited, 

 and always in far smaller quantities ; thus, for instance, I could 

 never obtain more than 2-g- of crystals from the blood of guinea- 

 pigs in the dark, whilst I was frequently able to procure more 

 than 7 of dry crystalline substance during ordinary daylight, or 

 in sunlight. That which has been already stated in reference to 

 light, applies very nearly with equal correctness to the application 

 of oxygen. We may not unfrequently succeed, even without the 



