SENSITIVITY of the bladder epithelium to carcinogenic stimuli was demontrated by the induction of cancer following the introduction of coal tar directly into the bladders of rats (Maisin and Picard, 1924;Picard, 1927). Bonser, Clayson, Jull and Pyrah (1953) showed that the implantation of relatively large paraffin wax pellets without added chemicals into the bladders of rats induced papillomas.On the other hand Rudali, Chalvet and Winternitz (1955) were unable to obtain tumours when small pellets of paraffin wax or cholesterol were inserted into the bladders of rats, but carcinomata were produced with wax or cholesterol pellets containing phenazine, 1: 2-5: 6-dibenzphenazine or 20-methylcholanthrene.The bladders of mice seem to be more resistant to the apparent carcinogenic; action of inert solids than are those of rats so that mice are more suitable animals for the testing of bladder carcinogens.Jull (1951) developed the technique of surgical introduction of wax pellets containing carcinogens into the bladders of mice and this has been used very effectively by Bonser, Clayson and Jull (1951) and by Bonser, Clayson, Jull and Pyrah (1952) in studying the induction of bladder cancer. These authors found that 2-naphthylamine, which induces bladder cancer in dogs and man, does not cause cancer when introduced into the bladders of mice. On the other hand pellets containing 2-amino-l-naphthol, which is a known intermediary metabolite of 2-naphthylamine, produced cancer of the bladder. Thus they showed that the method could give some indication as to whether a carcinogen was acting directly or after metabolic changes. The fact that bladder tumours were obtained with 20-methylcholanthrene and 3: 4-5: 6-dibenzcarbazole suggests that these polycyclic compounds act without undergoing previous metabolic changes.In the present work the technique described by Jull (1951) has been modified in two ways (cf. Boyland and Watson, 1956). Firstly, the substances under test are mixed with four parts of cholesterol and compressed into pellets instead of being mixed with molten wax. Secondly, the opening in the bladder through which the pellet is introduced is tied off with thread instead of being sewn. A disadvantage of this method is that some tumours are induced by cholesterol pellets alone and this must be considered in assessing the carcinogenicity of the substances tested. Bonser, Bradshaw, Clayson and Jull (1956), in a thorough investigation of this technique, obtained tumours in a proportion of mice treated with pellets of paraffin wax. This induction of cancer by chemically inert material is perhaps analogous to the induction of sarcomata by subcutaneous implantation *Present address: Brisban)e General Hospital, Brisbane, Australia.

No abstract

IT is generaflv agreed that prostatic cancer does not-develop spontaneously in rodents. Transplantable tuniours of the rodent prost-ate have been induce(i followinu iiioculation of the glaiid in situ with carcinogem, but the resulting growths h-ax-e been either sarcomas or squamous-cell carcinomas (Moore aiid Atelchionnal 1937 Dunning, Curtis and Segaloff, 1946; Horning and Dmochows, ki, 1947). ',---)'uch kinds-of prostatic cancer rarely occur, however. in man (AVillis, 1948 (Homing, 1946) The object of this paper is to trace in some detail the histogenesis of the induced prostatic carcinomas and to describe the influence of castration an(I -;;ex lioriiione administration on their growth. TECILNIQUE.The method of tumour induction consists in isolating small strips of prostatic epithelium from either the anterior, ventral or dorsal lobes of the gland, and m.-rapping the pieces of epithehum around crystals of 20-methyleholanthrene prior to grafting the whole subcutaneouslv into host mice of the same sex, age and strain. The fragments of epithehum were isolated under a dissecting microscope with the aid of an iridectomy knife. The carcinogen was then placed in contact with the surface of the epithelium, and ingerted into a Bashford transplanting needle, care being taken to shield the carcinogen from the connective tissues of the host animal. In some instances as manv as tbxee subcutaneous primarv grafts were made on each side of the belly of a s'mgle host mouse to give a series of prostatic tumours growing under identical hormonal conditions. The technique is similar in some essentials to that -previously employed bv Greene (1945), and Rous and Smith (1945), except for the important difference that the present experiments involved tiimour production from adult, not embrvonic tissues.The influence of bilateral orchidectomv upon the growth rates of glandular and squamous cefl prostatic carcinomas was mvestigated in 6-months-old mice, which had Pre'%iously been castrated before attaining pubertv. The tumours,

IN a previous publication Homing and Whittick (1954) described the histogenesis of stilboestrol-induced renal tumours in the intact male golden hamster, the development of which was first discovered by Matthews, Kirkman and Bacon (1947

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