Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/189

 made use of abnormal ones. The question whether the organs of animals may be used will be discussed later.

The organ must be absolutely freed from blood, a condition that can be attained in the case of different organs with varying facility. Placenta and lungs, for instance, can be easily washed so as to free them from blood, or the blood may be rinsed out through the large blood-vessels; whilst the liver, kidneys, and particularly the uvea, are freed from blood with great difficulty. With the latter there is scarcely any other means of proving its suitability, than by experimenting comparatively with serum from individuals with healthy and diseased uvea respectively. The pigment prevents us from discovering the last traces of blood.

The fresh and still warm placenta is first freed from blood clots by mechanical means, the membranes and the umbilical cord being removed at the same time. Then the placenta is cut into small pieces, about one inch square or less, and these are crushed in a current of water, for which purpose they are best placed on a sieve. Water is allowed to run continuously upon the pieces of placenta, each piece being pressed between the fingers. From time to time the pieces are placed in a cloth and squeezed in it. The washing of the placenta must never be