PHYSIOLOGY. 



C93 



culty of determining the blood-pressure in the 

 capillary vessels, remarks that the exact state 

 of the case can be determined only under ideal 

 conditions. In the current of an incompressi- 

 ble and inexpansible fluid through a system of 

 pipes under a given propelling force, the rate 

 of current is always in inverse proportion to 

 the cross-section, while, with the distance of the 

 propelling force, the pressure abates at a rate 

 proportionate to the distance i. e., it sinks 

 more rapidly in narrow, and more slowly in 

 wide, tubes. In the middle of the capillary 

 system, the pressure, according to known laws, 

 amounts to half the initial pressure. In the 

 circulation of the blood, the cross-sections of 

 only the larger arteries and veins are known; 

 the cross-section of the capillary system is un- 

 known. Under the ideal conditions, however, 

 this cross-section might be calculated from 

 measurable rates of current. Thus, it may be 

 calculated that the diameter of the capillary 

 system is 25 times, and the whole section 

 625 times, that of the aorta. The curve of 

 pressure sinks slowly in the arterial system ; 

 but in the capillaries, on account of the great 

 difference of pressure required by the great 

 resistance, it sinks very considerably, to sink 

 more slowly in the veins, till in the neighbor- 

 hood of the heart it becomes negative. In the 

 middle of the capillary system the pressure, in 

 accordance with this view, was equal to half 

 the pressure in the ventricle. Should the ar- 

 teries become narrower by contraction of their 

 smooth muscle - fibers, the point where the 

 pressure was equal to half the heart's pressure 

 would shift nearer to the arterial system ; if, 

 on the other hand, contractions or obstructions 

 occurred in the veins, that point would come 

 closer to the venous system. 



Various opinions have been arrived at by 

 different observers concerning the influence of 

 the organic constituents of the blood upon the 

 contractility of the ventricle, and as to whether 

 the heart can feed on its own tissues. Dr. S. 

 Ringer declares that, from experiments which 

 he has made upon the effects of different salts 

 on the period of contractility, he is " driven 

 to the conclusion that there is most probably 

 stored up in the muscular tissue material to 

 carry on contractions ; that this material can 

 not be washed out by a fluid circulating through 

 the cavities of the heart, and that the amount 

 of the stored-up material varies with the time 

 of year and the condition of the frog." From 

 other experiments he believes he can show 

 that blood or serum is quite inadequate to 

 maintain the heart's contractility unaided by 

 inorganic substances, such as lime and potas- 

 sium salts, in addition to sodium chloride and 

 an alkaline sodium salt ; but that, when the cir- 

 culating fluid contains a sufficient quantity of 

 these salts, a very small quantity of blood, 

 fresh or dried, serum, or milk, is sufficient to 

 sustain contractility for many hours. He has 

 : found that the effect of blood added to circu- 

 t lating fluid is not dependent on the fats it con- 



tains; that milk effectively sustains the con- 

 tractility of the ventricle ; and that gelatin 

 helps greatly to sustain it, but is decidedly in- 

 ferior to blood. Dr. Ringer also records the 

 results of his experiments with "tap-water" 

 (New River, London), which contains thirty- 

 eight parts per million of organic matter, when 

 substituted for distilled water in the circulat- 

 ing fluid. The effect was greatly to increase 

 the sustaining action of the fluid. Experi- 

 ments made to ascertain whether this superi- 

 ority was due to the minute quantity of the 

 organic matter contained in it, or to inorganic 

 constituents, showed that while circulating 

 fluid containing one part of dried blood in 12,- 

 000 will long sustain contractility, it is decid- 

 edly inferior to "tap-water" circulating fluid 

 containing only one part of organic matter in 

 25,000. Further experiments in detail showed 

 that much of the efficiency of " tap-water " is 

 probably but not entirely due to its lime sul- 

 phate. But experiments with artificial fluids 

 containing calcium sulphate and calcium bicar- 

 bonate failed to exhibit the positive results 

 afforded by " tap-water." 



The Digestive System. Prof. Ewald spoke in 

 the Physiological Society of Berlin, March 27, 

 concerning the occurrence of lactic acid in hu- 

 man gastric juice, which was now universally 

 regarded as a pathological formation, or a 

 product of fermenting processes which did not 

 obtain under normal conditions. In conform- 

 ity with this opinion he had, in a former paper, 

 clearly demonstrated the absence of lactic acid, 

 even after milk had been taken. On the other 

 hand, he had regularly found hydrochloric 

 acid in the gastric juice. From more recent 

 experiments which he had had opportunity 

 to make in cases of hysteric vomiting, he 

 inferred that lactic acid occurred normally in 

 the contents of the stomach, namely, in the 

 first period of digestion. It was, however, in 

 his opinion, no normal constituent of the gas- 

 tric juice, but, in the case of a mixed and meat 

 diet, originated in the carno-lactic acid ob- 

 tained from the meat, and, in the case of white 

 bread being taken, from the fermentation of 

 the starch. With reference to the ultimate 

 uses of lactic acid, the speaker agreed with 

 Prof. Maly, that it was employed toward the 

 formation of the free hydrochloric acid after- 

 ward appearing in the gastric juice. 



" The Lancet " calls attention to some phys- 

 iological facts in relation to drinking as of 

 much importance, because they concern the 

 promotion of health. Thus, it is essential that 

 there should be constantly passing through the 

 organism a flushing, as it were, of fluid, to 

 hold in solution and wash away the products 

 of disassimilation and waste. As fully three 

 quarters of the entire organism are normally 

 composed of fluid, there is evidently great need 

 of a copious supply of it. If there be not suffi- 

 cient endosmose, the exosmose must be re- 

 stricted, and effete matters, soluble in them- 

 selves, but not dissolved because of the defi- 



