Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/188

manner in which a substrate is prepared is of the greatest importance for the whole success of the dialysation process, and, unless one adheres to the directions in every particular, one is bound to meet with unsuccessful results. These, however, can be successfully avoided if the preparation of the substrate be carried out with proper attention. The principle of the matter is, to obtain substrates which contain coagulated albumen and are absolutely free from diffusible substances which react with ninhydrin. We shall demonstrate the method of obtaining the substrates by means of the preparation of coagulated placenta. Other organs are treated in exactly the same way; only, those which are rich in fats and lipoids have to be previously extracted with carbon tetrachloride in a Soxhlet apparatus. The same applies also to tubercle bacilli. Placenta can always be procured in a fresh state, whereas in other cases we have to deal with organs from dead bodies. In the latter case the dissection should be made at the earliest opportunity. The best corpses are those of accidents. If prolonged agony has been undergone previous to death, the organs are almost useless. It is very important to test the organs for pathological changes; and it is absolutely essential to state in what condition the organ used was found, for different results could easily be obtained if one observed used normal organs while another