348 Dr. A. du Pre Denning and Mr. J. H. Watson. [May 7, 



passage through fine capillaries than it does through tubes of comparatively 

 wide bore. 



During the consideration of the series of observations contained in 

 Table III we drew attention to the diversity of the results that might be 

 obtained with the blood of different animals, even though it contain exactly 

 the same number of corpuscles and the same amount of added salt or 

 anticoagulator. This at first sight may seem very contradictory ; but 

 remembering how the red cells vary in size not only in different species but 

 in the individuals of the same species, we would suggest, from considerations 

 of physical and natural phenomena, that this dissimilarity may be due to 

 quite small variations in the dimensions of the red cells and the amount of 

 the attendant colloidal matter {e.g., proteids, etc.) enveloping them as central 

 nuclei in much the same way as, for example, the solid and semi- 

 solid particles in brackish water are coated with slime, or as the planets 

 surrounded by their attendant atmospheres, or perhaps more nearly 

 resembling the richly colloidal Schaummassen and Schaumjiocken in 

 Professor Quincke's theory of colloidal solution.* 



And, indeed, here it might well be remarked that just as all purely 

 colloidal solutions which have been standing for any length of time tend to 

 become more viscous by reason of the growth of existing colloidal nuclei 

 and the formation of new ones at the expense of the colloidal materials in 

 the sustaining fluid medium, so we may similarly expect that a badly 

 circulating but otherwise healthy blood with the average amount of colloids 

 would, as a result of its partial stagnation, likewise tend to become more 

 viscous, and so, by thus still further decreasing the circulation through the 

 whole system, and more especially in the peripheral vessels, eventually give 

 rise to some form of cyanosis, unless counteracted in other ways. 



As showing the comparative unimportance of such changes to the rate of 

 flow through the veins and other large vessels, we give, in Table VI, a few 

 comparative values obtained with a tube of 3 - 5 mm. and a capillary of 

 - 6 mm. It has, of course, long been recognised that Poiseuille's law only 

 holds for homogeneous solutions in narrow tubes if the rate of flow be slow, 

 which certainly was not the case with the larger tube in question, as may, 

 perhaps, be inferred from the low value found for the plasma. But for our 

 purpose this is immaterial, since the result clearly illustrates the fact that 

 changes in the viscosity are only of importance in the circulation of the 

 blood through the finer channels of the circulatory system. For example, it 

 will be seen that, with a blood containing some 16 million red corpuscles 

 per cubic millimetre, the value for rj was only 5 - 3 times that for water at 

 * Cf., e.g., G. Quincke, ' Ann. d. Phys.,' vol. 9, pp. 969—1045, 1902. 



