Franklin P. Mall 249 
a moderately distended spleen is, as Table IV shows, 157,080 sq. mm., 
which multiplied by the length of a pulp space (0.02) gives 3 cc., a very 
insignificant portion of the entire volume of the spleen. 
It is seen then that there are variations in the relation of the main 
vascular trunks to the capillaries in different organs, as was intimated 
by Thoma. This ratio in the spleen, determined by comparing arteries 
0.05 mm. in diameter with capillary arterioles, is 287; in the lung it is 
9+ and in the liver it is at least 49. The sectional area of the capillaries 
of a lobule is 49 times that of the final portal twigs which supply the 
lobule. 
All the lobules are equally favored, as has been frequently asserted 
and is easily proved by making injections with fluids of various consist- 
ency into any of the three vessels of the liver. In each case all of the 
terminal vessels fill simultaneously. The lobule most distant from the 
main vessel is not less favored than the lobule near to it. Thoma’s 
laws have regulated the growth of the system of vessels and also have kept 
it adjusted. 
According to Thoma’s hypothesis, whenever the capillary pressure ex- 
ceeds a certain point due to an increased exchange of substance in the 
crowing adjacent tissue, there is a new formation of capillaries. Those 
portions of the area yasculosa which are favored later by the circulation 
seem to run ahead in their development in blastoderms from 18 to 39 
hours old. It is seen that accelerated growth is accompanied with the new 
formation of capillaries long before there could possibly be any circula- 
tion through them.” A similar condition is to be seen in the human 
embryo. The blood vessels arise in the walls of the umbilical vesicle and 
grow into the embryo and form the main circle of vessels within it before 
the heart is fully formed. Such a condition is to be seen in the embryo 
described by Eternod. In exceptional pathological conditions they may 
develop into the villi of the chorion without the formation of a heart. 
Loeb” has shown, by an ingenious experiment, that a very complete 
vascular system is developed in certain fish embryos without any cireula- 
tion of blood at all. He placed the eggs of Fundulus immediately after 
fertilization in a solution of sea water to which 14% of K Cl had been 
added, and found that they undergo a normal development without any 
heart beat: the chloride of potassium had paralyzed the heart. However, 
a complete vascular system is developed, being practically normal in ar- 
rangement within the embryo. as well as in the yolk-sac. The form 
2 Thoma, 1. ¢., p. 28. 
* Loeb, Pfliger’s Archiv., LIV, 1893. 
