Tissue Culture (q.v.). Minute portions of chick and duck em bryo heart have been cultivated in special glass cells. Under suit able conditions these portions of tissue live, grow and beat rhyth mically in the culture medium for prolonged periods. If two portions of heart from the same species are placed in the same culture cell, each beats rhythmically at an independent rate until the masses fuse by growth, when the beats become synchronous. If in the experiment the two portions are chick and duck, fusion by growth may occur but independence of rhythmic contraction persists.
Much of the research falling into this category is concerned with the minute physical chemistry of the cell and therefore is of a fundamental character though hardly suitable for analysis in this place. An important practical result of labora tory work consisted in a simplification of the method of preparing insulin (q.v.) whereby a larger amount of the material of a higher potency was prepared from a given amount of raw mate rial in less time and at smaller cost. Insulin forms a picrate when freshly ground pancreas is mixed with solid picric acid. The insulin picrate is extracted by acetone. By this discovery the cost of insulin treatment of diabetics has been reduced to one-third or less.
Perhaps the most striking subject upon which bio chemical investigations have been conducted during recent years has been that associated with accessory food factors (vitamins, q.v.) and food deficiency diseases. Investigation of beriberi (q.v.) a nutritional disease associated with various nervous and paralytic symptoms, which occurs in man and can be induced in pigeons by feeding exclusively on polished rice, showed that addi tion of a minute quantity of the milling was sufficient to prevent onset of the disease or cure it if in existence. Then followed in vestigations into the causation, prevention and cure of scurvy and enquiries into the factors underlying growth of the body generally or of special systems (e.g., bone in rickets). It cannot be said with certainty that rickets depends exclusively upon absence of a special vitamin, for other factors, such as a sufficiency of calcium and phosphorus, are necessary. Moreover, sunlight, particularly the ultra-violet portion of the spectrum, is no less essential than due provision of the requisite vitamins for production of that normal growth of the body of which normal growth of bones is but a part. As a result of the entire series of investigations upon accessory food factors, it may be said that at the present time fat-soluble vitamin A and water-soluble vitamin B are regarded as being bound up with processes of growth and in addition there are anti-scorbutic and anti-beri-beri vitamins and one that is necessary for fertility (see DIET AND DIETETICS). These vitamins
have been found in a great variety of animal and vegetable sub stances and the amounts present vary within wide limits. Their nature is unknown, and the most certain points in connection with them are the minuteness of quantity in which they are present and the potency of their activity. As to their origin the suggestion has been put forward on experimental grounds that they are com pounds of high energy content produced by the influence of ultra violet light, but this hypothesis cannot be regarded as proved ex cept in the case of vitamin D (anti-rachitic).
(see RADIOLOGY; RADIOTHERAPY; RADIUMTHER APY).—On its diagnostic side, quite apart from the use of contrast meals and injections opaque to the rays, it is now possible to pro duce far better radiographs with exposures measured in fractions of a second than were possible at the beginning of the century with exposures lasting minutes. This is largely due to the employ ment of X-ray tubes in which the anticathode is a mass of tung sten, heated by an independent current. For treatment, in order to approximate the wave-length of rays emitted by the X-ray tube to the wave-length of the gamma rays of radium, apparatus has been produced with a voltage in the region of 200 kilovolts. So far this type of apparatus is employed chiefly in the treatment of cancer. During the routine examination of large numbers of cases various anatomical peculiarities have been observed and some hitherto unknown morbid processes in bone have been de scribed. Radiology has also proved useful in study of the physi ology and pathology of the heart and great blood-vessels, in pul monary conditions, notably tuberculosis and bronchiectasis, in diagnosis of renal and biliary calculi, and it has been suggested as a means of diagnosis when perforation of a gastric or intestinal ulcer is suspected. The intentional injection of oxygen or air into the peritoneal cavity as an aid to radio-diagnosis has been employed somewhat extensively; it is stated to be devoid of risk and renders diagnosis of fluid or solid masses relatively easy. The use of radium (see CANCER; RADIUM) is confined chiefly to the treatment of cancer.