Neoplastic invasion as seen in the rat Rd/3 neoplasm has been studied electron microscopically in three sites: abdominal wall, footpad and liver. This neoplasm invades by peripheral cell division and active cell migration. Neoplastic cells protrude many fine processes and compress host cells. Neoplastic cells invade lymphatic vessels in a way similar to that in which white blood cells penetrate them - by the protrusion of fine cytoplasmic processes and passage, sometimes in clumps through open cell junctions. There is no ultrastructural evidence of secretory phenomena.

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SUMMARY The activities of 13 enzymes in 40 carcinomas of the large bowel have been studied using histochemical techniques. Five enzymes-non-specific esterase, monoamine oxidase, succinate dehydrogenase, cytochrome oxidase, and acid phosphatase-commonly show much less activity in the tumours than in adjacent normal colon. The tumours have been classified based upon the number of enzymes which show marked reduction in activity in each tumour (types 1-5). The enzyme histochemical type and the size of the tumours have been jointly correlated with the presence of lymph node metastasis. Small type 1 or 2 tumours do not appear to be associated with metastatic disease. Small type 5 tumours were commonly associated with secondary carcinoma in the lymph nodes. Large tumours (greater than 25 sq cm surface area) of any histochemical type were frequently associated with lymph node metastasis. Discussion of the possible reasons for these findings and their clinical significance is presented.Previous histochemical studies of the enzymes in proliferative conditions of the large intestine have been primarily concerned with detecting possible differences between benign and malignant neoplasms (Wattenberg, 1959a and b;Nachlas and Hannibal, 1961;Czernobilsky and Tsou, 1968). Although information on the enzyme histochemistry of rectal and colonic carcinomas is available from such studies, the extent to which the enzyme histochemical patterns vary between tumours and the clinical significance of such variability has not been studied.The purpose of the present work was to examine in detail the frequency and possible clinical significance of the enzyme histochemical differences between individual carcinomas of the large bowel. Materials and MethodsTissue from 40 patients with carcinoma of the large intestine was studied.Within 10 minutes of resection, the intestine was opened and irrigated with saline and pinned out. A perspex viewer was placed over the tumour and adjusted so that the undersurface of the viewer touched the tumour surface without compressing it. The outline of the tumour was drawn on the perspex. This outline was transferred to tracing paper and subsequently to 1 millimetre Received for publication 14 March 1973. squared graph paper. The areas within the outline were measured by planimetry. Small tumour areas were checked by counting squares on the graph paper within the outline. Blocks of tumour and adjacent mucosa were snap frozen in liquid hexane at -70C using solid CO2 and absolute alcohol mixture as coolant. Serial frozen sections were cut at 10 m,u. Two sections, one test and one control, were mounted directly onto each slide. The sections to be used for the study of the hydrolytic enzymes were postfixed in acetone at 4°C for one hour. The remainder were allowed to dry at room temperature for five minutes. Thirteen enzymes were studied in each of the 40 tumours. The sections were incubated in the appropriate media using the open perspex ring technique (Chayen, Bitensky, Butcher, and Poulter, 1969).The histochem...

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