254 COMPARATIVE. HISTORICAL. 



there is increased activity of metabolism, increase in muscular energy, increased 

 appetite, subjective feeling of warmth. The pulse is slower, and the pulse-curve 

 lower. 



On account of the invigorating and stimulating effect of a sojourn in moder- 

 ately compressed air, the employment of the latter has been practised for thera- 

 peutic purposes ; and it has been found that repeated applications have produced 

 favorable after-effects of considerable duration. Unduly rapid increase of pressure 

 is to be avoided and likewise unduly rapid removal of the pressure. 



Waldenburg and others have constructed apparatus in the form of a spirom- 

 eter; either compressed air maybe inspired from its bell-jar, or the bell- jar may 

 be filled with rarefied air, into which the expirations are made. Both methods 

 are used in suitable cases for therapeutic purposes. 



Paul Bert has found at an excessively high, artificial atmospheric pressure, 

 over 30 vol. per cent, oxygen in the arterial blood of animals (investigated at 

 700 mm. of mercury). If the amount of oxygen reaches 35 vol. per cent., death 

 occurs, accompanied by convulsions. At a somewhat lower point the bodily tem- 

 perature falls, the oxidation-processes in the body are reduced, strange to say, 

 and as a result of this the formation of carbon dioxid and urea is diminished. 

 Greatly compressed oxygen also produces the effect of a relative deficiency of 

 oxygen; animals die in it, exhibiting signs of suffocation with greatly reduced 

 metabolic processes. 



Frogs exhibit in compressed oxygen (up to 14 atmospheres) the same phe- 

 nomena as they would in a vacuum or in pure nitrogen. There occurs paralysis 

 of the central nervous system, at times preceded by convulsions. Then the heart 

 stops beating (but not the lymph-hearts) , and at the same time the motor nerves 

 lose their irritability; finally, the direct muscular irritability disappears. 



Under exceedingly high pressure of oxygen (thirteen atmospheres) an excised 

 frog's heart beats scarcely one-fourth the time that it remains active in the air. 

 If the quiet heart be brought into the air, the pulsations may return. Under a 

 pressure of 100 atmospheres the frog's muscles still contract normally, and only 

 at 400 atmospheres do they become paralyzed. 



Phosphorus ceases to be luminiferous under high pressure of oxygen, but not, 

 however, the phosphorescent organisms, for example, the lamprey, or the phos- 

 phorescent bacteria, such as those of meat (micrococcus Pflugeri). Exceedingly 

 high atmospheric pressure is injurious to plants also. 



COMPARATIVE. HISTORICAL. 



Mammals have lungs similar to those of man. Those of birds exhibit a spongy 

 structure; they are fused with the inner surface of the chest-wall, and have, on 

 their outer surface, openings that lead into large, thin- walled air-sacs, lying among 

 the viscera. These air-sacs further communicate with the cavities in the bones, 

 which contain air instead of marrow, in order to provide greater lightness (pneu- 

 maticity of the bones). There is no diaphragm. In reptiles the lungs are divided 

 into larger and smaller divisions of vesicles; in snakes one lung atrophies, while 

 the other becomes greatly drawn out and elongated, in accordance with the form 

 of the body. Frogs pump air into their lungs by contraction of the pharyngeal 

 sac, the nostrils being closed and the larynx opened. Turtles fill their lungs with 

 air by a sucking movement. Amphibia (frog) possess two simple lungs, each of 

 which in its structure to a certain extent represents an enormous infundibulum 

 with its alveoli. When young (until their metamorphosis) they live as aquatic 

 animals, and breathe by means of gills; the perennibranchiates (proteus) indeed, 

 like the fishes, breathe in this manner throughout life. Among fishes the dipnoi, 

 besides their gills, possess a swimming-bladder, abundantly supplied with afferent 

 and efferent vessels, constituting an internal respiratory organ remotely comparable 

 to the lungs. By the term "gills" is meant an organ for respiration in water, 

 constructed in the form of numerous, vascular, plate-like diverticula. Among the 

 fishes, the mud-fish (cobitis) exhibits an intestinal respiration, when there is lack 

 of water and it buries itself in mud; in this process air is swallowed on the upper 

 surface of the water, the oxygen is abstracted in the intestines, and carbon dioxid 

 is discharged through the anus. Insects and centipedes respire through tracheas, 

 which consist of numerous air-canals distributed throughout the body and com- 

 municating with the atmosphere on the outer surface of the body by means of 

 openings (stigmata) that can be closed. As insects possess no true circulatory 

 movement of the blood, the air conducted through tubes penetrates from all sides 



