460 



SECRETION. 



being received into the circulating current ; 

 that being eliminated by the kidneys, in the 

 state of health, as fast as it is formed, it has 

 no time to accumulate in the blood ; but that 

 when such elimination is checked or dimi- 

 nished, whilst its formation continues, the 

 minute quantity originally present gradually 

 increases, so as at last to become easily de- 

 tectible by chemical processes. However 

 probable such an explanation might be felt to 

 be, it is yet satisfactory to find it confirmed 

 by direct experiment.* Simon and Marchand 

 some time since obtained satisfactory evi- 

 dence of the presence of urea in the healthy 

 blood of the cow ; and Dr. Garrod has lately 

 succeeded in obtaining urea from the serum 

 of healthy human blood. The amount, as 

 might be anticipated, was very small, only 

 l-200th of a grain of urea being procurable 

 from 1000 grains of serum. f 



The pre-existence of uric acid in the blood 

 might in like manner be inferred from the 

 well-known fact of its deposition in gouty con- 

 cretions : this inference, also, has been con- 

 firmed by Dr. Garrod, who has discovered 

 uric acid in the blood of gouty subjects. It 

 might be not unreasonably asserted, however, 

 that the presence of uric acid in the blood is 

 the result of a disordered condition of the 

 system generally ; and it is hence satisfactory 

 to find that in this case also Dr. Garrod has 

 succeeded in obtaining the substance itself 

 from healthy blood. He states that the 

 amount seems liable to considerable variation, 

 and to have some relation to the period that 

 has elapsed since food was last taken, being 

 least where this was longest : thus in one in- 

 stance, where food had not been taken for 

 twenty-four hours, 1000 grains of serum 

 yielded only 2-1000ths of a grain of uric acid ; 

 whilst a similar quantity of serum from the 

 blood of other healthy subjects yielded 

 7-1000ths ; and a like amount of serum from 

 the blood of a man of full habit, but other- 

 wise healthy, yielded 37-1000ths of a grain 

 of uric acid. 



Of hippuric acid, which exists in small 

 quantity in human urine, but in much larger 

 amount in the urine of herbivorous animals, 

 Dr. Garrod states (loc. cit.) that he thinks he 

 has detected traces in the blood. 



There can be no reasonable doubt that 

 kreatine and Jereatinine are normal elements of 

 healthy blood, since they are constituents 

 of the "juice of flesh," which seems to be the 

 result of the disintegration of the muscular 

 tissue, and must be taken into the circulating 

 current to be conveyed from the muscles into 

 the urine, where we again meet with these 

 substances. 



In like manner it is probable that lactic acid 



* Dr. Prout states (On Stomach and Renal Dis- 

 eases, 5th ed. p. 531. note), that when engaged in 

 examining the blood in the year 1816, he found 

 urea (or a substance having most of its properties) 

 in that fluid ; but not crediting the fact, and think- 

 ing it might be accidental, he did not pursue the 

 enquiry, though he made a memorandum of the 

 circumstance. 



f Lancet, July 8. 1848. 



is normally present in the blood in very mi- 

 nute proportion ; for it abounds in the juice 

 of flesh, and must be taken into the current 

 of the circulation, in order to be eliminated 

 from the body. In the healthy state it seems 

 to be eliminated through the respiratory 

 organs as fast as it is generated; being con- 

 verted by oxidation into carbonic acid and 

 water. It was formerly supposed to be a 

 normal constituent of the urine; but it has 

 been clearly proved by Liebig not to have a 

 real existence there. Even when lactate of 

 potash has been introduced by the stomach, 

 the potash is thrown out by the kidneys in 

 combination with other acids, the lactic 

 acid not being eliminated in the urine, but 

 passed off through the lungs. In certain dis- 

 eased states of the system, however, lactic 

 acid unquestionably presents itself in the gas- 

 tric, urinary, and cutaneous secretions ; and 

 as it has been shown to be one of the results 

 of the disintegration of the muscular tissue, its 

 pre-existence in the blood cannot be reason- 

 ably doubted. 



The less definite nature of the constituents of 

 bile prevents them from being as certainly re- 

 cognised in the blood as those of urine have 

 been ; nevertheless, the evidence of their pre- 

 existence in the circulating fluids is sufficiently 

 clear. Thus cholesterine may be obtained 

 from the serum of the blood by an analytical 

 process of no great complexity ; and its pre- 

 sence there is also manifested by its occasional 

 deposit, as a result of diseased action, in 

 other parts of the body, especially in the 

 fluids of local dropsies, as hydrocele, ovarian 

 drops}', &c. Again, the colouring matter of 

 the bile seems to be nearly identical with 

 certain normal elements of the blood, since 

 the hue exhibited by a departing ecchyrnosis 

 is identical with the characteristic colour of 

 bile. In cases of jaundice, the presence of 

 the colouring matter in the blood is often 

 made evident, not merely by the communica- 

 tion of its peculiar hue to the several tissues 

 and secretions of the body, but also by the 

 tint visible in the serum of the blood itself. 

 It would seem probable, however, that in 

 many of these cases there has been an actual 

 re-absorption of the biliary matter subse- 

 quently to its elimination by the liver, as a 

 consequence of obstruction to its exit by the 

 gall duct. But in the most severe and ra- 

 pidly fatal cases of jaundice, as pointed out by 

 Dr. Alison*, the secreting process has never 

 taken place, and the colouring matter must 

 then have been generated in the blood itself. 

 Neither cholesterine, nor the colouring matter 

 of bile, seem to exert the poisonous influence 

 on the nervous system which is manifested in 

 the cases alluded to ; and it is probable that 

 this must proceed from the accumulation of 

 the peculiar organic constituent of the bile. 

 As the precise nature of this, however, is still 

 a matter of discussion amongst chemists, we 

 cannot be surprised that it has not yet been 

 obtained by analysis from the blood. 



* Edinb. Med and Surg. Journ. vol. xliv. 



