attack, we are policed by myriads of zealous leucocytes, ever ready to reduce the invaders to impotence. The germs which have found entrance fire off a toxin. The leucocytes reply with an antitoxin. There is absolutely no limit to the power of protoplasm to protect itself, if only it be not taken by surprise. It can resist any organic poison if it is allowed a sufficient time to produce the antipoison. The ferment of pancreatic juice, trypsin, is a poison which is unlikely to find its way into the blood. When injected it produces disastrous results owing to its immense activity in digesting proteins. An animal “prepared” by the injection of successive doses of trypsin develops an antitrypsin. Injection of pancreatic juice no longer does it any harm. Tapeworms which live in the intestines are bathed in pancreatic juice; they are constantly exposed to its digestive action. They are not digested, because they secrete an antibody which prevents the development of the activity of trypsin. It is not in this case, strictly speaking, antitrypsin. It is antikinase, a substance which, if extracted from the bodies of tapeworms and added to pancreatic juice, renders it incapable of digesting albumin. The antikinase does not destroy trypsin, but destroys kinase, the co-operation of which is essential to its activity. Not only has protoplasm the power of meeting with an antiferment any ferment which might prove prejudicial to its own integrity; but after it has been once attacked it continues to defend the vulnerable spot. Its tactics are, it must be confessed, somewhat like those of the dusky warrior who, during his first lessons in the art of boxing, made a point of covering with his fist the place where he had just been hit; but even its power of remembering its last injury is of supreme value to the human race. Before the age of sanitary science, and even, in certain backward communities, in these days of its beneficent rule, conditions producing disease were not necessarily set right as soon as the epidemic was over. The close-packed inhabitants of a ghetto were continuously exposed to germs of typhoid fever, small-pox, whooping-cough. But after their protoplasm had once responded to the need for the production of an antigerm, it either continued for many years to keep a stock in hand, or it kept the recipe within easy reach. The memory of protoplasm is amazing. It is commonly said that vaccination is an absolute protection for seven years. There is no doubt but that the immunity from small-pox which it induces, if gradually lessening, lasts for life. The disease, if it attacks a person who has been vaccinated in infancy, is relatively harmless.