PUBLIC SCIENTIFIC LECTURES.

Globe, Volume V, Issue 557, 31 March 1876, Page 2

PUBLIC SCIENTIFIC LECTURES.

Last evening the second of the series of public lectures on scientific subjects was delivered in the Oddfellows’ Hall by Dr Powell, who chose as his subject “ The Wanderings of a Blood Globule.” The lecturer commenced by stating that if a man cut himself he bled. This appeared now-a-days like a truism; but only 300 years ago, prior to the discovery of the circulation of the blood by the illustrious Harvey, the cause of this simple fact was enveloped in complete mystery. If by the cut a large blood vessel were divided the man bled until he fainted, when the blood ceased flowing, but recommenced on consciousness being restored; and if assistance were not'at hand, bleeding would continue until the final loss of consciousness passed into death,

On the other hand, dead animals when cut did not bleed, and even if a large bloci vessel were divided, the escape of blood would be very inconsiderable. What was the nature of the blood ? If a drop of blood were placed beneath the microscope, it was seen to be a colorless fluid in which floated myriads of minute biscuit shaped bodies, called blood globules, or more correctly, corpuscles, these each having a diameter of three thousand five hundredths of an inch, and a faint tawny tint. A teaspoonful of blood would contain more globules than there were inhabitants in the world. The globules differed in form and size in different animals, those low in the scale of organisation having larger corpuscles than the more highly endowed. The globules had a great affinity for oxygen, which entered into feeble chemical combination with them, so feeble that they parted with it in a vacuum. Oxygenated blood was of a bright scarlet, but when deprived of its oxygen became of a purplish black. An average man had from 121 bto 151 b, or about l£ gallons of blood in his body. The circulating organs consisted of a system of closed tubes, of which the heart formed the centre. The lecturer then described the course of the blood vessels, illustrating his remarks by reference to a diagram. Tracing on the diagram the course of the blood vessels to the point of the finger, he illustrated their transition into capillaries, by showing a beautifully prepared section of an injected finger tip, by the aid of the oxy-hydrogen microscope. Having followed the veins back to the heart, he described the structure of this organ, demonstrating its system of valves by diagram and by specimens prepared from a bullock’s heart; he showed that the movement of the blood could only be in one direction from the veins towards the arteries. The lecturer directed attention to a preparation of a a sheep’s heart, which had glass tubes fixed in the vena cava, and the pulmonary artery. On squeezing the right ventricle with his hand so as to imitate its contraction, he caused a coloured fluid to pass from the one tube into the other in the direction of the normal circulation. On connecting a small hand pump with the tube fixed in the artery the valves opposed regress so as to cause the artery to swell up nearly to bmsting. Dr Powell then alluded to the elasticity of the arteries, which though not very great was very perfect, its object being to convert the intermittent action of the heart into a continuous flow, and he illustrated this by exhibiting Dr B, W. Richardson’s spray producer, showing how by means of an elastic reservoir a continuous jet could be produced by a single stroke of the pump. He said that were the arteries rigid tubes no capillaries could resist the force of the heart, and bleeding would ensue from every pore. It was by these means that the circulation of the blood was kept up, a single globule completing the circuit in twentythree seconds, or about twenty-eight strokes of the heart. n the screen he showed injected preparations of the synovial membrane of the knee joint, a frog’s foot, the ciliary process of a horse’s eye, and the longitudinal section of a cat’s tongue. What did the blood do ? Why should it be thus driven into every corner of the system ? Its office was to carry oxygen from the lungs—to burn up the the tissues of the bsdy—thus generating animal heat, and carrying with it the products of combustion, the most important of which physiologically was carbonic acid, which, if it accumulated in the blood to a very small extent, caused death. After dwelling on this topic for a short time, the lecturer proceeded to describe the eccentric behaviour of the white globules ; these consisted of protoplasm, and curing life were continually changing their form, growing, moving, dividing, and even feeding, as might be demonstrated by mixing a little solid carmine with the blood ; yet until within the last few years they had been represented by microscopists as mere inert globules, the fact being that they had observed only dead white globules, killed by the cold to which they were unaccustomed. He described their behaviour when the process of inflammation was going on, stating that they penetrated the walls of the capillaries, and accumulating and multiplying in the tissues formed matter. Dr Powell concluded his lecture by exhibiting on the screen an injected section of a rat’s brain, showing its extreme vascularity. He stated that during deep thought the capillaries of the brain were turgid with blood, whereas during calm sleep the brain was comparatively bloodless. The brains of his audience were at present in the prior condition, and he hoped that that state of temporary congestion Would be followed by that pleasant ancemia which conduced to a night’s rest. In plainer English he had the honour to wish them “ Good night ” At the close of the lecture, as well as during its delivery, Dr Powell was much applauded.