Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/203

 committed against the fundamental rules of the whole method, that errors are bound to occur. Therefore, we must not ignore a method because it requires careful working. It is quite possible that with time we shall arrive at more simplicity in our manipulations, and technique may place some further means at our disposal. But it is as yet too early to try to introduce modifications in the manner of working of the two methods, after a whole number of observers have obtained good results by their means in their present form. The principal requirement of any method is, that we should not rest until the cause of error is found in each case that occurs. This is the only way of avoiding them.

First of all blood is taken. If there be any doubt regarding the suitability of the substrate it is advisable first to test the organ, so as to avoid withdrawing the blood unnecessarily. This test should be repeated immediately before performing the experiment. The blood is allowed to coagulate spontaneously at the temperature of the room.

Immediately before beginning each experiment the organ is tested, and this important rule must never be neglected. It may so happen that all the parts of an organ have been freed from all extractive substances reacting with ninhydrin, except a piece here or there. It should be the duty of the observer to note down each time in his record: "Organ tested."