low but steady rate as long as the energy for the beat is supplied solely by hydrolytic processes; but there is certainly no change in the physical structure of the cells noticeable in _Fundulus_, and consequently there is no sudden standstill of the heart. Budgett has observed that in many infusorians visible changes of structure occur in the case of lack of oxygen[301]; as a rule the membrane of the infusorian bursts or breaks at one point, whereby the liquid contents flow out. Hardesty and the writer found that Paramœcium becomes more strongly vacuolized when deprived of oxygen, and at last bursts. Amœbæ likewise become vacuolized and burst under these conditions. Budgett found that a number of poisons, such as potassium cyanide, morphine, quinine, antipyrine, nicotine, and atropine, produce structural changes of the same character as those described for lack of oxygen. As far as KCN is concerned, Schoenbein had already observed that it retards the oxidation in the tissues, and Claude Bernard and Geppert confirmed this observation. For the alkaloids, W. S. Young has shown that they are capable of retarding certain processes of autoxidation. This accounts for the fact that the above-mentioned poisons produce changes similar to those observed in the case of lack of oxygen.[302] [301] Budgett, S. P., _Am. Jour. Physiol._, 1898, i., 210. [302] Loeb, J., _The Dynamics of Living Matter_, New York, 1906, pp. 19-21. The phenomenon of rapid disintegration when deprived of oxygen (or in the presence of KCN) seems to be general as Child[303] has shown in extensive experiments. Child has used it to show that younger animals disintegrate more rapidly than older or larger ones, and he uses this fact for a theory of senescence. He connects the more rapid disintegration of the young animal with a greater metabolism.[304] Without wishing to doubt Child’s interesting observations the writer is not quite certain whether the more rapid disintegration of the younger forms is not a result of the fact that the walls of membranes in the young are softer than those of the older animals, and hence are more readily liquefied. Such a difference could be due to mere chemical constitution, _e. g._, the increase in Ca in the membrane with the increase in age. In old age in man the deposit of Ca in the blood-vessels is a frequent occurrence. [303] Child, C. M., _Senescence and Rejuvenescence_, Chicago, 1915. [304] It is a fact that in the early cells of _Ctenolabrus_ the dissolution of the cell walls through lack of O precedes death, since when oxygen is admitted early enough the cells recover again. In infusorians the bursting of the animal due to lack of O occurs suddenly, while the animal is still moving, and this bursting is the cause of death, and not the reverse.