224 J. B. JOHNSTON, 
mingles its secretion with that fluid. WALDScHMIDT (87) attributes 
the same function to the saccus in Polypterus. DE Cyon (98) in 
an experimental investigation on the hypophysis of Mammals finds 
that pressure or electrical stimulation produces immediate variation 
of blood pressure with noticeable augmentation of the heart. His 
explanation of this as the result of a reflex effect upon the thyroid 
by way of the X nerve, I do not understand. He further attributes 
to the hypophysis the production of a chemical agent similar to 
iodothyrine, which acts on the heart in the same way as does the 
iodothyrine, and upon the vagus and sympathetic in such a way as 
to protect the brain. 
In some of the large blood vessels of the brain of the common 
bullhead (Cottus) stained by the intra vitam methylene blue method, I 
have found isolated cells similar to the ciliated cells of the saccus. These 
were found in the winter of 1896—97, since which time I have not 
been able to give them further study. At the same time I found 
fine nerve fibres in the walls of the same vessels. I believe that 
both structures are part of an apparatus governing the blood pressure 
in the vessels of the brain. Fibres in the walls of the blood vessels 
of the pia which probably have a similar function have been de- 
scribed by HuBER (99) in Mammals. 
The apparatus in the saccus probably has a similar function. 
There are in the saccus all the conditions of an efficient organ 
for supplying the cerebro-spinal fluid: an expanded sac with 
numerous subdivisions, offering a large surface over which the 
cerebro-spinal fluid is separated from lymph by a thin membrane; 
and an epithelial lining containing sense cells whose afferent fibres 
presumably set up connections with the cells of origin of the efferent 
fibres which enter the saccus from the inferior lobes. I have not 
made out the central connection between the afferent and efferent 
fibres but it seems probable that they constitute a reflex apparatus 
in which the efferent fibres play the part of secretory fibres. The 
saccus may also produce indirect effects on the action of the heart 
and on blood pressure by way of the X nerve. The fibres passing 
caudally from the cells of the end nucleus of the saccus bundle 
(page 115) are probably the means of making connections with the 
vaso-regulator mechanisms in the medulla. 
