672 PATHOLOGY OF PARTURITION. ' 



unaccompanied by pain. There must be some particular reason for this. 

 We know that the vaso-motor centre, and more especially the vaso-motor 

 nerves, together with the distention of the vessels, are greatly influenced 

 by the sensory nerves, because of a reflex mechanism which exists be- 

 tween them \ as we know to be the case, on a larger scale, between the 

 sensory and motor nerves. As a rule, irritation of the sensory nerves is 

 followed, first by contraction, then by great dilatation of the vessels, 

 which may even lead to extravasation in some cases. The tendency to in- 

 flammation and its results must also not be lost sight of. It might be 

 imagined that the pains at birth would have the effect of expanding the 

 vessels, to admit of the flow of blood driven out of the gravid uterus. 



It has been remarked by nearly every authority, that calf-fever ensues 

 after quick and easy parturition, when but little assistance has been re- 

 quired. In such cases there can be but little pain, and therefore one 

 would expect little, if any, distention of the vessels. But it is just in 

 these cases of easy parturition that a particularly severe aortic distention 

 arises ; as at times the uterus contracting too quickly, causes a mass of 

 blood to be suddenly propelled into this vessel. At other times, the 

 whole vascular system is unprepared for the mass of blood forced into it ; 

 consequently, the aortic pressure reaches its higl^eslr degree. The ques- 

 tion now presents itself : Are there, then, anatomical- indications to show 

 clearly why the disease in question should be so prevalent among cattle, 

 whilst with the other domestic animals it occurs but seldom, or not at 

 all ? Such indications exist, as a matter of course. The process of con- 

 veying blood to the brain of cattle — particularly to that of ruminants^is 

 a peculiar one. The Cow has no single large vessel — no carotis i?iterna — 

 to convey blood to the brain, as is the case with the Mare, but a number 

 of small vessels which penetrate to the cranial cavity. These vessels, 

 however, do not spread over the surface of the brain, as in the Mare ; 

 they form a sort of network — the rete mirabile — from both sides of which 

 a branch develops itself, and which forms the proper brain arteries. The 

 following seems to be the result of the peculiar distribution of the ves- 

 sels : 



I. The circulation of arterial blood to the "brain is very uniform ; 2. Ir- 

 regular pressure in the aortic system cannot easily, and then only slowly, 

 be transmitted to the arteries of the brain. Now, however. Bidder's ex- 

 periments have shown that sudden increase of blood-pressure does not 

 produce any comatose symptoms, but that these always set in if the in- 

 creased pressure is of any duration. Under these circumstances, brain 

 oedema is much more likely to set in than if the blood pressure were to 

 disappear quickly. 



The anatomical arrangement of the rete mirabile is such that it chiefly 

 supplies the cerebrum. This should tend to explain why, in eclampsia of 

 the Cow, the comatose symptoms are so common that convulsions seem 

 exceptional. It is an interesting fact that, in Swine, this fever is often 

 observable in. those in which the rete mirabile is greatly developed. Not 

 long ago, Wall ey ( /^/m/^«r/a«, 1874) asserted that this so-called calf-fever 

 was dependent on this peculiar distribution of the vessels. 



Practically, as yet no illness has been observed, such as attacks the 

 Cow and Mare, where the flow of blood to the brain is direct, and con- 

 veyed through large vessels. As in the latter, the flow of blood to and 

 from the brain is rapid, a check in the circulation sufficient to cause 

 brain oedema and anaemia is with difficulty effected. In the Mare, in- 



