74 Mayow 



particles which are also elastic. So that there should 

 be no doubt at all now that an aerial something 

 absolutely necessary to life enters the blood of animals 

 by means of respiration. And indeed if the necessity 

 for breathing arose, as some have imagined, merely from 

 this that the mass of the blood should be churned and 

 divided into the most minute parts by the movement 

 of the lungs, there would certainly be no reason why 

 an animal, enclosed in a glass vessel in the manner 

 described, should die so soon, because the air there 

 avails as much after the death of the animal as before 

 to inflate the lungs and consequently to churn the 

 mass of the blood. For as that air is impelled by 

 the pressure of nearly the whole atmosphere, there is 

 nothing to hinder it from being urged into the dilated 

 thorax of the animal, and on this the inflation of the 

 lungs depends, as we have shown elsewhere. 



There is now no reason therefore for denying the 

 entrance of air into the blood because on account of 

 the dulness of our senses the vessels by which it enters 

 cannot be seen. For other ducts which serve to 

 convey thicker liquids are not seen by the eye until 

 their different capillaries,'after a passage of some length, 

 unite in a noticeable canal. For what keenness of 

 vision has ever beheld the sources of the lymphatic or 

 lacteal vessels or even of the veins ? How much less 

 may one discern these aerial ducts which must be very 

 short and extremely small, for these ducts do not, like 

 the others, run any considerable distance and at last 

 join one another, but merely pass separately by a very 

 short and obscure route through the membranes of 

 the lungs ; for that the aerial particles should be mixed 

 with the blood in the minutest and most intimate way, 

 it is necessary that they enter the blood by vessels or 

 rather pores almost infinite in number, distributed, here 



