l6o THE HISTORY OF BIOLOGY 



he recorded his experiences may perhaps be found in his lack of capacity 

 as a writer; indeed, from the point of view of style his papers were not of 

 a high standard, his exposition being often unclear and at times almost 

 impossible to understand. 



Malpigbi's investigations 

 Of Malpighi's writings the first in point of time and undoubtedly the most 

 important as to contents is the short account, in the form of two letters 

 addressed to Borelli, of his investigation of the structure of the lungs. In 

 the first of these essays he declares that the substance of the lungs had till 

 that time been regarded as "fleshlike," which was incorrect; the lung con- 

 sists rather of a network of extremely thin-walled cells, which are connected 

 with the finest ramifications of the windpipe. This, he states, can best be 

 observed by flushing out with water the blood from a fresh lung, then in- 

 flating the lung through the windpipe, and afterwards drying it. In con- 

 nexion with this discovery he advances some speculations with regard to 

 the function of the lungs, which he assumes to be to keep the blood flowing 

 and to prevent it from coagulating, which happens when it has run out of 

 the veins. He also discusses the high temperature which fever produces in 

 the blood and considers it to be due to a process of fermentation. In the 

 second letter he gives an account of the finer structure of the lung of the 

 frog, and in connexion therewith he describes his discovery of the capillary 

 circulation as a connecting link between arteries and veins, which he also 

 observed in the frog. In order to demonstrate this vascular system he recom- 

 mends that a frog's lung be inflated, then dried, and in that state examined 

 under a magnifying-glass. He himself emphasizes the importance of the fact 

 that the transition between the venous and the arterial blood had been dis- 

 covered, and posterity has confirmed the truth of his discovery. The achieve- 

 ment that comes next in importance is his investigation of a series of organs 

 which he placed in the category of the glands. These investigations he carried 

 out partly with fresh material, partly with such as had been hardened by 

 cooking, besides which, by means of injections into the blood-vessels and 

 the preparation of the tissues, he endeavoured to trace the minutest elements 

 of the organ. In the liver, with which he started his investigation, he thus 

 followed the blood-vessels up to their finest ramifications, which he con- 

 nected with a mass of small protuberances which may be brought up on 

 the cooked liver. By establishing the existence of these he considered the 

 liver's glandular character proved, which modern science has shown to be 

 correct, although the small protuberances are actually pure outgrowths 

 without any equivalent in the true structure of the liver. Malpighi also in- 

 cludes in his investigations of glands his observations of the cortex of the 

 cerebrum. He observed in this organ the pyramid-cells, which he believes 

 to be glandular elements that secrete the ' fluidum" whereby the muscles are 



