INTRACRANIAL AND INTRAOCULAR FLUIDS 



1769 



table I . Distribution in the Rabbit of 

 Various Ions and Nonelectrolytes 



[After Davson (59)] 



table 2. Distribution of Chloride and Bicarbonate 

 in Various .Mammalian Species 



[From Davson and Luck (58, 63)] 



* Between aqueous humor and plasma; t between cere- 

 brospinal Quid and plasma; t between plasma dialyzate 

 and plasma; where R represents the ratio between the con- 

 centration in fluid water and the concentration in plasma 

 water. 



Figures in parentheses are assumed values, no measure- 

 ments being recorded in the literature. 



centrations of bicarbonate, potassium, phosphate, cal- 

 cium, glucose and urea arc less than in such a dial- 

 ysate. In the rabbit, to which the figures in table 1 

 apply, the concentration of magnesium in the cerebro- 

 spinal fluid is the same as in the dialysate, but in man 

 the concentration is considerably higher so that the 

 ratio R r . 8f is of the order of 1.13 (156) to 1.30 (137). 

 Owing to the binding of magnesium to the plasma pro- 

 teins as an unionized complex, the value of R^m, the 

 distribution ratio for a plasma dials sate, is 0.80; in 

 man, therefore, the cerebrospinal fluid has a very large 

 excess of magnesium over that in a dialysate of plasma. 

 The aqueous humor of the rabbit is characterized I >\ 

 obvious excesses of bicarbonate and ascorbic acid, 

 by comparison with a plasma dialysate, while chloride, 

 calcium, glucose and urea are deficient. These fea- 

 tures of the chemical compositions of the two fluids 

 are sufficient to emphasize that both may be re- 

 garded as secretions in the sense that osmotic work 

 must be performed during their elaboration. The 

 results described in table 1 apply to the rabbit, the 

 only species in which an exhaustive study of the two 

 fluids, drawn from the same animals, has been carried 

 out. With the exception of the distribution of mag- 



* Between aqueous humor and plasma; f between cere- 



luiispinal fluid and plasma. 



nesium, discussed above, the chemical composition of 

 the cerebrospinal fluid does not show wide variations 

 with differenl species, in the eye, however, some 

 striking species variations in the distributions of 

 certain substances, notably chloride and bicarbonate, 

 have been lound, as shown in table 2. 



It will be seen that in the guinea pig and rabbit the 

 distributions of chloride arc such that the aqueous 

 humor has a deficiency of this ion by comparison 

 with a dialysate of plasma ( R , , , , ] averages about 

 I.04), while the horse, don, goat, etc. have excesses 

 of chloride; in general, those species exhibiting an 

 excess of chloride show a deficiency of bicarbonate, 

 although the cat and dog have small excesses of 

 both ions. A clue to these variations in distribution of 

 chloride and bicarbonate is given by plotting the 

 value of the distribution ratio for chloride against the 

 weight of the eye, as in figure 10. It will be seen that 

 there is a broad correlation between eye size and the 

 magnitude of the ratio — i.e. the magnitude of the 

 excess of chloride in the aqueous humor — the largest 

 excess being found in horse and ox eves. The cerebro- 

 spinal fluids of all species, from the rat to the horse, 

 have chloride and bicarbonate distributions corre- 

 sponding roughly with those characteristic of the 

 aqueous humor of the large-eyed animals. If we 

 regard the cerebrospinal fluid as the typical cavity- 

 filling fluid, then we may say that the aqueous humors 

 of the small-eyed guinea pig and rabbit have under- 

 gone some modifications to meet the special require- 

 ments of small eyes. As to what all these requirements 

 are is not immediately evident, but one becomes 



