Physiology

Therapeutic Use. Other forms of radiant energy, sunlight (heliotherapy), mercury-vapour quartz lamp, carbon arc, radiant heat, all of which depend upon the presence of ultra-violet light in the first instance and warmth in the second, are employed ther apeutically to an increasing extent. A disadvantage under which X-ray and ultra-violet forms of treatment labour is the absence of a satisfactory standard of dose. Sabouraud's pastille is only reliable for "soft" radiation. The "skin erythema dose" is un satisfactory because as used in France it is two and a half times as great as the "Hauterythemdosis" of the Germans. Even in German institutions the erythema dose varies between 285 R units and 1,120 R units (Martius).

Effects of Radiation. Numerous researches have been made on the effects of radiation, particularly the gamma rays of radium, upon cells and tissues of the animal body, plants, seeds, bacteria, protozoa. It has been shown that the cell in division is more vulnerable than the cell at rest and that there exists a wide range of radiosensibility amongst animal cells and tissues. Amongst the most radiosensitive are the lymphocytes. So far as composite tissues are concerned the intestinal mucosa is highly radiosensitive, exposure of the abdomen to unduly heavy dosage leading to excessive formation of mucus, mucoid degeneration, intestinal haemorrhage, paralysis of intestinal muscle, desquama tion of large tracts of mucosa and death from toxic absorption. While there is universal agreement that, directly or indirectly, rays produce injurious effects upon cells there is doubt whether smaller doses do not stimulate the activity of cells.

Histology.

Morbid histology has been in some measure at a standstill, although during the World War it was employed ex tensively in striving to unravel the pathology of trench nephritis, gas gangrene, gas poisoning and, indeed, of any novel pathological condition. Its most striking success was in reference to the mode of extension of gas gangrene from the seat of infection. The action of the toxin secreted by the infecting bacilli extends along the muscle bundles far in advance of the bacilli themselves, pro duces glassy changes of the muscle fibres correlated with a loss of contractility that can be demonstrated on the operation table and is a necessary precursor to advance of the bacilli themselves by multiplication. These observations were the prelude to a rad ical modification of the surgery of the condition and a definite im provement in results.

Bacteriology.

In bacteriology (q.v.) a useful step was taken by the Medical Research Council in forming the national collec tion of type cultures at the Lister Institute. Begun in 192o it now contains more than 2,000 living strains of bacteria, protozoa and fungi, available for workers in widely different lines of research.

Experiments upon the conditions under which bacilli, particu larly the sporing anaerobes of tetanus and gas gangrene, exert pathogenic activity showed that, if washed clear of toxin and inoculated without contaminating substances, they remained inert. Multiplication, followed by manifestation of the ordinary disease phenomena, occurred only if they were injected along with toxin (not necessarily their specific toxin) or with some solid particles such as lime or silica. In other experiments the presence of silica exerted an important influence on the multiplication of tubercle bacilli in the tissues.

Diphtheria.—Important observations were conducted in many countries upon the so-called Schick test as a means of diagnosing susceptibility to diphtheria (see INFECTIOUS FEVERS). If a minute quantity of diphtheria toxin, highly diluted, be injected intrader mally in man, there occurs a patch of redness locally about 2 cm.

in diameter in certain persons, whereas in others the injection is without effect. Heating of the toxin destroys its power of produc ing this effect. Further search indicated that in those persons who are negative, diphtheria antitoxin is present in the blood serum, whether naturally, or as the result of having passed through an attack of diphtheria, or of gradual immunization owing to the fact that the person is a diphtheria carrier. In Schick-positive persons there is absence of antitoxin and therefore the injected toxin is not neutralized and produces its pathological effect. Sub sequent examination on a large scale showed that the reliability of the test was of a high order. The natural corollary is that during an epidemic all Schick-positive persons should receive a prophylactic treatment with diphtheria antitoxin. Later work showed that diphtheria "anatoxin," i.e., toxin detoxicated by ad dition of formaldehyde and exposure to a temperature of C for a few weeks, was equally efficacious in producing immunity.