654 



PHYSIOLOGY. 



elusion, he would not regard it as proved until 

 it has been tested by experiments made on the 

 pleural cavity directly or within the lungs them- 

 selves. Besides the relations to the breathing of 

 the upper parts of the lungs, the condition dis- 

 covered to prevail in the upper part of the me- 

 diastinum has an important bearing on the 

 question of the respiratory undulations of the 

 blood pressure. During the inspiration both 

 venas cavae and right auricle are, so it is gener- 

 ally assumed, under a considerably lower pres- 

 sure than the veins outside of the thorax, which 

 difference of pressure causes greater inrush of 

 blood into the great thoracic veins and the right 

 auricle, and thus more blood comes into the 

 ventricle, etc. ; the expiration, on the other 

 hand, by the diminished intrathoracic negative 

 pressure diminishes the influx of the blood into 

 the 'ventricle. The same conditions have, it is 

 calculated, an opposite but a smaller effect on 

 tho aorta. It appeared in the experiments that 

 the inspiratory changes in the intrathoracic 

 pressure are very small in the upper part of the 

 mediastinum, the main change in the pressure 

 occurring in the lower part of it. As the up- 

 per part reaches as far down as the fifth or sixth 

 rib, so this part contains the entire superior 

 vena cava, the arcus aortae, the auricles, and a 

 considerable part of the inferior venae cavae, and 

 the descending aorta. In short, the main cir- 

 culatory parts which are expected to be influ- 

 enced by the considerable change in the intra- 

 thoracic pressure are located in that part of the 

 mediastinum where, according to the author's 

 experiments, very little change occurs. Dr. 

 Meltzer contents himself with a short paper re- 

 ferring to the subject, awaiting a confirmation 

 of the facts he has stated. 



Experiments to determine the effects of abla- 

 tion of the thyroid gland in the dog are de- 

 scribed by M. B. Gley. Hitherto all who have 

 performed this operation on the dog, cat, and ape 

 have found that the result was almost invariably 

 fatal ; and in the few cases where it is reported 

 that life has been preserved, the author considers 

 that the successful issue has been due to the 

 presence of accessory thyroid glands which have 

 acted vicariously, and that where the animals 

 have survived for a considerable time death has 

 been really due to the operation, although the 

 connection with it has been overlooked. The 

 experiments of M. Gley, who describes the symp- 

 toms in detail, confirm this view ; and although 

 they do not afford any clew to the function of 

 the thyroid gland, they seem to demonstrate the 

 remarkable influence that the removal of the 

 organ exercises on the nervo-muscular apparatus. 



It has long been a disputed question whether 

 light, by direct action on animal tissue, can in- 

 fluence the carbonic acid excretion as it influ- 

 ences the oxygen excretion of a plant by direct 

 action on the chlorophyll of the leaf. The ex- 

 periments that have been relied upon in support 

 of the hypothesis of such action are shown by 

 Carl A. 'Ewald to be liable to some objection 

 that prevents their being regarded as conclusive. 

 Mr. Ewald, by using frogs which had been cu- 

 rarized, avoided errors from any indirect effect 

 of light on the muscles, and from the possibility 

 of post-mortem changes, and was able to deal 

 with typical animal tissue which can be directly 



exposed to the light. He then made seventeen 

 series of three observations each, the average of 

 which showed a ratio of carbonic acid excreted 

 in the light to that produced in the dark of 100 

 to 98| ; throwing out two of the series in which 

 an apparent explanation was found for the in- 

 creased excretion in the light, the ratio became 

 100 to 99 that is, a difference of only 1 per 

 cent., which is less than the probable error of 

 the experiment. From this it may fairly be 

 concluded, he says, that in the case of a curarized 

 frog, when the possibility of muscular action is 

 eliminated, light does not in any appreciable 

 way affect the carbonic-acid excretion. 



With regard to the revival of animals after 

 exposure to great cold, Herr Kochs points out 

 two things which retard formation of ice in the 

 natural body. First, the body does not contain 

 pure water, but salt and albumen solutions which 

 freeze only under zero C. Herr Kochs says that 

 water in a glass tube of from 0'3 to 0*4 millimetres 

 diameter may be cooled to 7 C., and even 10 

 C., without freezing. With a diameter of from 

 only 0-1 to 0-2 millimetres the water is not frozen, 

 even though the end of the tube be put in freez- 

 ing liquid. The liquid sheets between two glass 

 plates behave in the same way. If a salt solu- 

 tion freezes, the salts are excluded ; and pure 

 water, in freezing, gets rid of its absorbed gas. 

 Fresh blood, according to the author's experi- 

 ments, freezes only after being strongly cooled to 

 15 C., and after complete elimination of gases 

 and salts. The blood-corpuscles are dissolved 

 and the blood loses color. The same elimina- 

 tion doubtless occurs in freezing of protoplasm. 

 Experiments cited show that the possibility of 

 " anabiosis " may probably be explained by sup- 

 posing the decomposition process not to have 

 gone so far as to bring life completely to a stand- 

 still. Similar results were obtained in the dry- 

 ing of seeds, and in various animals. It was 

 shown with what tenacity many animals, under 

 most unfavorable circumstances, retain the moist- 

 ure necessary to life. 



In respect to the synthesis by plant cells of 

 the albuminous matter which serves for the 

 formation of protoplasm, O. Loew holds that the 

 living protoplasm is composed of proteids en- 

 tirely different from the ordinary soluble pro- 

 teids, as well as from the proteids of dead proto- 

 plasm. In other words, if living protoplasm 

 dies, the albuminous constituents change their 

 chemical character. We observe that in the liv- 

 ing state a faculty of antoxidation (respiration) 

 exists, which is wanting in the dead condition; 

 and Pfliiger, in 1875, drew from this the conclu- 

 sion that in protoplasm the chemical constitu- 

 tion of the living proteids changes at the moment 

 of death. Among the considerations that in- 

 duce acceptance of this logical conclusion are the 

 readiness with which chemical changes occur in 

 organic compounds that are of a labile character, 

 and certain experiments cited by the author to 

 show that the albuminous substance formed by 

 synthesis in living plants is different even be- 

 fore it has become protoplasm from ordinary 

 albumen. On treating living plant cells with 

 dilute solutions of ammonia or organic bases or 

 their salts, either numerous minute granules are 

 formed or else little globules are produced, which, 

 flowing together, make relatively large drops of 



